Check If Email Exists | Hacker News Reader

Check If Email Exists

github.com

479 pointskilodeca250 comments

Could someone spell out a use case for this? One that comes to mind would be validating that a mailing list doesn't have any outdated email addresses in it, but couldn't that be determined by just checking for a bounce when a message is sent to it?

I tried to sign up for SiriusXM the other day, and though I could create an account with my .pro email address, I couldn't actually sign up for service with that same address for some reason. It's frustrating that validating email addresses is still something that people get so wrong. Please just take whatever seeming garbage I've entered into your email address field and try to send a message to it.

(Their site also had stupid password generation rules such that I couldn't use the 21-character one my password manager auto-generated, but even after I made one that followed the rules on the page, it was still rejected because there were apparently rules on the back end that weren't spelled out in the front end. Please hire me, SiriusXM.)

I receive a lot of fake user signups on the web tool I publish for free. These users (bots?) sign up using fake email addresses, but putting a captcha does not help much. I send a confirmation email to these users to make sure they exist, but if the email address does not exist, sending that confirmation email hits my account's deliverability (spam) score as it generates a bounce which my email sender provider does not appreciate.

For example, I've received multiple warnings from Intercom that I need to improve deliverability of my email, or they will ban my account. Ironically one of the suggestions is to use confirmation emails - but that's exactly where the problem is for me.

A tool like this helps me to weed out a ton of these undeliverable email addresses to avoid sending emails that will hit my spam score.

> checking for a bounce

So in my case, generating that bounce is exactly what I need to avoid in order to make sure my account remains in good standing.

I think what this is telling you is that users don’t value giving you their email address for your free tools. They know why you want their email address, and they don’t want that, but they do want your tools. Maybe it’s time to charge money for those tools or change models? Maybe not give access until the email address is confirmed? Worth considering I guess. Idk the details. I do this all the time. Ads and malpractice have made giving out your email address risky business. If a user can give you a fake email and get what they want without giving you anything (subject to your ads or whatever you’re using their email for) that’s the logical thing for them to do.

Not judging or anything though I know my tone might seem that way.

You seem to be assuming there's no reason these tools need a login system at all. Assuming they do and they're storing some kind of state or data for the user, how do you handle forgotten passwords if the user can't receive an email? A second free tier for people who can't be bothered to add a recovery email is too much work for a tool that's free anyway.

To the parent: Just send a validation email during the onboarding process. Don't create the account until they validate. And DO rate limit the number of these sent to any given address and the number of signup attempts by IP / fingerprint. Captchas are also good, but just for slowing fakes down.

> Just send a validation email during the onboarding process. Don't create the account until they validate.

This is literally the same thing the person you're replying to suggested.

Is it that risky? Talking, at least, as a somewhat knowledgeable person, which is the target of such web tools.

I usually have no problem using my email address to sign up for things. And yes, I do know that emails will come.

Sometimes they are actually useful and I keep them. Often, I don't care and I just unsubscribe. I some not-so-common cases, it is spam, in which case I mark it as such and I am never bothered by it again.

Sure, it's a bit of extra work. But I would not classify it as risky business.

I was thinking risky in terms of cost/benefit.

The cost for me to give a fake email is very close to 0, and the risk of getting spam emails or who knows what is much higher in comparison so why bother giving anyone my real email address? I mean I do give it out from time to time (you can easily find it if you want) I’m just speaking generally.

Issues I've had is after x years or some leak a ton of mail start pouring in.

You seem to be assuming “a lot of fake user signups” == “few real user signups.” OP only said the first. For all we know they also get plenty of real ones.

Weird. Same exact 5-word opening I was typing. I didn't see your post until I posted mine.

Great minds think alike? Heh

If you dont state clearly why you even need the emails, fake one is the way to go.

If a tool like this works for you, what stops you from sending validation emails yourself?

I'm not the OP, but the answer is typically

1) Time, and..

2) Deliverability

Home grown email systems require monitoring (e.g. deliverability rates, IP reputation monitoring) and maintenance of the system itself which can be a time sink.

The reality is without using SES, Sendgrid, or a similar 3rd party provider, avoiding people's spam folder is very tricky.

A non-marketing example:

We were onboarding a large new client to our SAAS product. This process involved creating accounts for all of their employees (tens of thousands) and sending emails with an activation link. (Where they'd be able to set up their password.)

Our system sends these emails in batches, and as soon as the first batch went out we got an alert from our monitoring system that our bounce rate was surging - high enough to risk a sending pause from Amazon SES. We stopped sending and investigated the issue, and it turned out that the email list we were given was a mess - it included all current employees, but also a huge number of former ones. Just under 1/10th of the emails in our first batch were invalid.

We asked the client to give us a better list, but due to internal issues they couldn't get that to us any time soon. Meanwhile they were breathing down our necks to get these emails out ASAP, and they were a large enough client that our management wanted to keep them happy, so we tried out one of these email validation services. Unfortunately, it didn't work. It turns out that this technique doesn't work for all mail servers. It was reporting every email as valid, even ones we knew were invalid since they'd already hard bounced.

(Edit: thinking back - this was several years ago - I think it wasn't saying that they were valid emails, just that it couldn't tell whether they were valid or not - the service was able to detect that the server wasn't rejecting non-existent addresses.)

We ended up unpausing the emails and just hoping for the best. Ended up with something like an 8% bounce rate that eventually fell off our record as our normal sending patterns resumed. Amazon's guidelines say they might cut you off when you hit 10%, so we cut it pretty close.

This is clearly trying to solve a non-technical problem with technical means. The root problem is that AWS cancels you with too high bounce rate. The obvious solution is to talk to some AWS representative to at least temporarily not cancel you after explaining the situation. If AWS does not let you talk to them, then that's where the problem lies, not in some not cleaned up email list.

It's terrible to spend a lot of effort on this kind of tech just because some business partner has shitty customer support.

But that would affect all customers of Amazon SES because the IP addresses would score low by other email servers.

Assuming that the customer's servers were hosted by some SaaS like Office, right?

If customer was hosting e-mail servers themselves they wouldn't notify any other mail servers?

> This is clearly trying to solve a non-technical problem with technical means.

Isn't that the whole point of what most of us are doing?

Is it? In my dayjob I'm solving technical problems with technical means.

World hunger is not a technical problem. You won't solve it with technical means. If you think you can, you have already lost the fight.

Climate change is not a technical problem. You won't solve it with technical means. If you think you can, you have already lost the fight.

And so on, and so forth. Technical means can help solving certain components needed for the overall solution. These are then technical (sub)problems though. For example, how to store more energy in a battery, or how to grow certain crops with less water. But the overall problems are social in nature. People need to understand that world hunger is a distribution problem. That one is easier to solve with certain (technical) tools available, but that won't be enough. People need to understand that we can't use more natural resources than get replenished. Not a technical problem. If only the tools get better, people will find new ways to be wasteful. Etc etc.

Climate change is technical problem. Carbon sequestering coal plants can remove all carbon from the atmosphere. World hunger is undoubtedly not a technical problem though.

World hunger is rapidly being solved by exactly technical means. So is climate change. How do you think these issues are solved?

World hunger is caused by power imbalances. That's a social/political problem. Whatever technical solution you provide helps worsening the root cause and at best keeps the status quo.

We have observed dramatic technical advances in all fields related to food production in the last 3 decades. We've seen at best marginal improvements in world hunger in the same time, and even that only if you're beeing optimistic with your statistics.

If they're checking using SMTP's VRFY command then it's actually considered a best practice for the server to always reply with a 252 "cannot verify" since otherwise it can be used to fish for valid addresses.

But... I could also fish for valid addresses by trying to send an email and waiting for a bounce...

Yes, and you could be eg: graylisted. Or server could accept all an silently drop. Or rate limit.

It's sad that VERIFY is basically dead due to spam. In the olden days, you might have been able to use finger - but it's also dead for (among other) similar reasons.

The spam cat and mouse game leads to quite silly situations for benign actors.

For some mx's you might be able to designate some ips as trusted, and do real verify for those.

I can't even imagine wanting to handle managing accounts and credentials for that many users at an enterprise! At that point SSO integration is well worth the money. How did you handle removing access when a user was no longer employed at the company?

Not OP, but also building a similar user system. I can totally understand the motivation to not use the internal SSO. With most companies I know, as soon as you actually connect to their private datasources, you have to do some extra steps to prove how you're securing your platform. This makes sense from the companies perspective, but also introduces a huge technical and organizational overhead for the startup which might be better spend elsewhere if your product does not absolutely rely on SSO

It seems like the most practical solution to that should be calling AWS, explaining it for 5 min, and getting an exception. Is that kind of reasonable solution no longer possible with the cloud providers being so huge?

It's possible, you just need to pay the extra 10% for premium support.

At that point would it not be easier to just spin up a VM in customer's infra and send emails directly to their exchange server?

Ok, so first pass gives me a TERRIBLE idea, that would "get the job done". I'm sure you thought of this and dismissed it:

Keep your "overall bounce rate" low, by ALSO sending out extra emails to confirmed email addresses. Like, for every "confirmation" email, also send a "thanks for joining us" email to someone that already confirmed their email.

I'd hope you'd at least be able to explain the situation to your account manager and get an exception(maybe for that single companies domain?), but I've never used AWS so I wouldn't know if thats possible.

account manager? you fancy.

TAMs you get with the higher support plans can be of some help in situations like these.

Why did all the employees have email addresses from different services, rather than a single @ourcompany.com address pool that they controlled?

This is a reason you need an escape hatch from SES.

In the past when I worked on a system that needed to notify via email we always had a way to change delivery process for certain emails, domains, etc for exactly this reason. This is one of those cases where we would “deliver directly” (i.e. send directly to their mail provider).

I’ve never worked with emails, could you not send these first emails yourself and not use SES

Have you looked into what SES or other email services provide? Sending emails is easy, while actually getting them delivered is harder. You have to make sure you're not getting flagged as spam, can handle bouncebacks, etc.

Here's one discussion: https://stackoverflow.com/questions/371/how-do-you-make-sure...

In GP's case, they probably could'e arranged with the client's sysadmins to whitelist the IP they were sending emails from.

Not getting flagged as spam isn't actually that hard, though. Besides, if you're using SES or some other hosted SMTP service, you still have to set up SPF for your domain, so you haven't even really gained much comfort. The only really useful thing is to gain an ip address with a high reputation, but you can generally get those at any reputable hosting provider as well. Just don't try sending emails from your residential internet connection.

Ah I understand that part but if it’s going to a big client who knows the emails are coming is it besides the point? I understand day to day

Wouldn't the better solution have been to support SSO?

The use case is marketing email. Sending to non-existent addresses can radically affect deliverability.

If the address is to a large host, then they will use reaching invalid email addresses as evidence that you are not keeping to best practices. They will throttle deliverability, and possibly reject email.

If your sending to an invalid host, then your mail sending provider (if your using one) may consider you a bad customer and send you through a lower grade of outbound IP addresses.

Frequently new registrations are processed at once as batch imports from another system or from a partner. There is a need to remove these invalid email addresses pre-sending and hurting sending reputation.

Any engineer or product team that uses this lacks ethics and is putting their company at risk for CANSPAM.

If you work at a company that would abuse hibp and a direct mention in CANSPAM you should refuse the work.

This is not for “marketing emails”. This is for spammers.

They’re the same thing, really.

Not really: but majority of spammers think that they are doing marketing.

And majority of marketing is perceived as spam.

we're on the cusp of defining a new internet law here

All marketing emails are spam, most spam is marketing emails.

What grinds my gears, is a company which has "important info" emails you cannot opt out of, but then it is still 95% spam.

My bank tried this during the start of the pandemic. Yeah, that kind of scummy.

"How to get CERB! Also, we're awesome and here are products to help you!"

(cerb == initial canadian relief payments)

Scum.

I've never once received a "marketing email" that wasn't spam.

Used to be in the same camp, before starting my own company. While the border is thin, it is clear, and there is a difference between marketing and spam.

I think you proved the point: when the spammer send spam they think they are doing marketing.

I don't know about you, but I'm subscibed to several newsletters out of my own volition.. Are they spamming me then?

> I'm subscibed to several newsletters out of my own volition.. Are they spamming me then? reply

No, since you signed up on your own volition, obviously they are not unwanted emails.

But I always uncheck the newsletter etc. box and still get tons of them. From legit companies. That's spam, and goes straight to junk mail.

If that was the case, all newsletter senders in the world are spammers too. And all spammers thinking they are marketers is not logically equivalent to all marketing is spamming

Fair enough, if I opt-in it isn't spam.

I have! Expensify. Not a customer, and never have been. Signed up because I was considering using the service. The emails are exceedingly infrequent and delightful to read.

That’s you (and the large part of HN who doesn’t know anything about normal users). When GDPR came into effect, we even had people write us that they were annoyed having to reconfirm, as obviously they still wanted our newsletter.

Some people want to receive marketing emails. The exact same emails are spam to the rest of us. If you default opt-in users and don't make blanket unsubscription from all marketing emails easy (and make the clear distinction [both internally and externally] between emails regarding the existing functionality of products/services that we've already paid for and emails to ask for more revenue from us, which includes copy supported by advertisers), then you're a spammer, simple as that.

Spammers aren't necessarily evil, but definitely annoying, and annoying customers is a good way to lose them. It's easy to drink the coolaid and eat the dogfood when you're paid to like it or have a passion for creating it but potential customers have roughly the opposite incentive and it pays to remember that.

I receive a lot of unread, unwanted email from companies I pay money to every month. It's ridiculous.

> If you default opt-in users and ... then you're a spammer, simple as that.

There is no "and". If you default opt-in users, you're a spammer.

> Spammers aren't necessarily evil

What?

There's some things right on the edge, like Netflix as an example. They're never trying to sell me anything; they've got my $N/month. The emails (that I don't read until now to sample them) are suggestions of shows I might like. User retention mail and promoting the shows they own the rights to are spam, but not all of it is.

My credit union sends infrequent warnings about recent phishing and scam techniques. I never opted in to those emails but they're not useless for everyone and possibly do net good.

I think a good heuristic is to look at the value provided in emails; if the recipient stands to benefit significantly more than the sender (on average) then it's not spam. Sure, my credit union has to deal with less hassle reversing charges or resetting passwords but it's quite a lot more hassle to be a victim of phishing or other scams.

Every few months, or when there's a big disaster, I get spam from Unicef, trying to get me to donate more money.

The emails are undoubtably spam, but (in my opinion) Unicef itself isn't an evil organisation.

I have a common name first year/generation gmail account. The volume of mail I receive that I didn't solicit is mind-boggling. Not just spammers, but it's obvious that people have saved the wrong address in their browser suggestions, and that people give it out when asked for an email addresses at retail. Disney employees, California private school parents, iPhone receipts and apple IDs. Taxes, warrants, bail bonds, social security information. People are f'ing stupid when it comes to email.

Everything should require a confirmation before you assume it's valid. Not because it doesn't exist but because it might not be who you think it is.

Yup, nobody wants those emails. Unfortunately sales people and marketers are excellent liars and they convince higher ups that it's worthwhile.

I agree with all you said. But there are many comments on HN that are "all marketing is spam in general".

If you’re sending to someone who actively subscribed and wants to hear from you it’s not “marketing”, it’s information. Basically a newsletter.

Otherwise it’s spam.

Only “marketers” make that distinction.

I don't know if it's always spam, but it's up the same creek as trying to brute-force your way into someone's heart.

I maintain a small fee tool for creating API endpoints to trigger email alerts for yourself (varmail.me). Since it's very basic and has no marketing, it doesn't get too many users. You have to click a link in an email to even log in, but I still get bots stuffing my login form with known bad email addresses (I've googled and some of them appear in honeypot lists). There is no chance they can get in, but this is bad because my login verification emails look like spam, since a large percentage of them are sent in response to these bots. So I definitely see some value in a way to pre-screen the emails there.

Interesting project, maybe you need a captcha to display and weed out bots before you actually send an email.

Yes, I've considered it. The thing is I really dislike captchas so I tried to avoid deploying one. I do have a hidden form field that gets populated with a secret value in JavaScript, so the bots must be running JS at least to function.

Personally, I do this kind of thing manually if I want to send some positive feedback to people who work at companies I like, but they don't have any obvious emails published.

A recent example was the CEO of Evernote for the work put in to their behind the scenes series although I don't expect anyone to read it of course. People are busy!

I wrote a bit about it here: https://utf9k.net/blog/email-lookup/

Now does this scale? Not at all and I haven't read the email spec or anything like that. It's also handy in a pinch if you wrote down an email but can't remember if it's spelled correctly or not.

The non-interactive nslookup for Windows invocation:

  nslookup -query=mx evernote.com

Edit: Trying out the macOS/Linux invocation on Windows also works:

  nslookup -q=mx evernote.com

Oddly, the first time I did this, I only got IPv4 results, subsequent queries for the same domain, included IPv6 as well.

For email confirmation.

The practice of email confirmation is still widely used, but the change in email deliverable rules has make it a pain to properly validate them.

Even if you are using a 3rd party provider like SES or mailgun, they have a email bounce limit. A considerable number of real world users give fake email address(which is even sometimes encouraged on HN) which triggers those bounce limits.

To fix it, there are paid services but they does not work very well. Fixing it yourself take a lot of engineering time, that is better spent elsewhere.

Providing an open solution to this problem (which is given in the github repo) is a double edge sword. As this gives a edge to spammers who created the problem in the first place.

I just watched a video where someone demo’d GitHub Copilot by writing a comment along the lines of

    // IsValidEmail takes a string and returns whether it’s a valid email address

The AI response was a nightmarish 100+ character regex that made my blood curdle.

I think of email validation like encryption: don’t roll your own, and don’t trust an AI to do it either.

Edit: Here's the regex: https://gist.github.com/cassidoo/6101ef0657665683b787aab5ae9...

100+ is nothing.

This is a regex that validates a string against the RFC822 "Standard for ARPA Internet Text Messages" and it contains 6424 characters.

http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.html

This is a Tony the Pony situation almost.

This really seems like it is plagiarizing the regex from somewhere without citation.

It looks like it:

https://twitter.com/xooorx/status/1410776673985994754

https://stackoverflow.com/a/38137215

all AI is plagiarizing something, though. Computers cannot reason, they can just jam stuff together that satisfies whatever the program says.

ML is matrix math (generally) - stuff that you can do by hand, computers are faster at it. As fancy as GPT and co-pilot are, it's all copied from somewhere.

Does it work?

Yeah basically, but it doesn't validate an email address (user@example.com), it validates say, the From: header of a MIME message, which could contain an email address, a phrase (like a first and last name) comments, and all sorts of dumb dumb ideas like having phrases that have embedded comments and phrases that look like email addresses but aren't and on and on and on. This RFC is a trainwreck and whoever wrote it should feel bad about themselves.

>but couldn't that be determined by just checking for a bounce when a message is sent to it

The fewer times you bounce, the better your chances of not being marked as a spammer.

This could also be useful for an ecommerce site, where you want to be able to easily contact the buyer if there's a delay, address correction needed, etc. People typo their own email at a rate that's surprising.

I use email validation via MailGun for exactly this purpose with a productized service business. If we don't have a good email, then we can't deliver the service once complete. That leads to angry customers, even if the issue was a typo when they created the account. Easier to try and catch it during signup rather than at the time of delivery when emails start bouncing and you have no way to get ahold of the person.

Mailcheck is also helpful to catch things like "user@gnail.com" and other common typos when the user types it in:

https://github.com/mailcheck/mailcheck

Fork modified for React: https://github.com/eligolding/react-mailcheck#readme

I somewhat lol'd when the demo allowed "user@gnail.com" just fine. Guess kickstarter isn't using mailcheck anymore. Looks like it's an open issue:

https://github.com/mailcheck/mailcheck/issues/179

Oh, yeah, that's not good. Not sure why they didn't just repoint to the suggested https://codepen.io/ianneub/pen/BajKKBy demo.

I bought a new car a few years ago and I was unable to enter my .life email address into the SiriusXM registration form in the car. Had to use a .com address :(

I specifically bought a cheap .org since some companies have trouble with lesser known TLDs

I have a hyphen in the domain (.com) I use for personal email (it's shorter, just my initial and surname) and I still have had problems in some places with that - it's so frustrating.

I have a .red and a .me and I have never not been able to sign up.

.life has four letters. Lots of terrible attempts to validate email addresses reject TLDs that aren't 2 or 3 characters.

>Lots of terrible attempts to validate email addresses reject TLDs that aren't 2 or 3 characters.

which is sad because .info has been around for 20 years.

pipesandcigars.com let me sign up with a .miami but now I can't login because it says it's invalid. My ISP frantically called me up after starting service because they took all my info down and then the system didn't like the domain. My utility company kept sending me requests to go paperless and I had to call them to get an answer on why that happened since I had accepted the paperless prompt, the issue was the domain.

It's nice to have but I've had quite a few headaches with it

I had a similar experience with LG. You need a developer account in order to install applications on webOS TVs. I successfully registered on the LG Developer portal with something like myname+us.lgaccount.com+2021-07-01@mydomain.com, but I couldn't log in on the TV with that email address. Had to register again without the plus signs.

I had something worse(?) happen with one of my accounts for a hotel chain. I entered name+hotel@majoremail.com and they just stripped out the + leaving me with an account that I couldn't use unless I made another account at the email provider.

Same, got a .email tld, and regularly get rejected.

Forget about AI and self driving car, we can't even get email validation right in 2021.

I am not sure there is any clear legitimate use for deep validation (beyond checking for syntax). If you are providing a valuable service to a customer, wether it's a catch-all or free mail shouldn't matter to you.

Now, if you are buying lists here and there to spam the hell out of it, the bounce rate would flag you very quick and you'd need to find another smtp provider every week. This service would be your life line.

Ideally you don't want to send an email only to find out it doesn't exist, in terms of marketing.

Do that too often and servers can start black listing your domain/IP because it looks like you're "scanning" for available email addresses.

Similar experiences here. I have [myfirstname]@[mylastname].party as my primary email. In meatspace it’s a curiosity, and people are sometimes incredulous. Online, I’m routinely given some variant of “enter a valid email address.”

We have been auditing legacy user accounts to begin a mapping to Zendesk, and Zendesk allows mapping to ‘organizations’ via email domain.

For some of these legacy accounts, the registered email addresses may have typos.

So, even a basic DNS check against the existence of the domain’s MX record is helpful.

Any of the ‘suspect’ email addresses can then be further evaluated by a human, and then removed or fixed.

Any kind of technical email validation is horribly unreliable at best and there is no chance that this GitHub repo is going to work any better.

As a result the only place such a service is useful is for someone who has a ton of low-value emails they don’t trust, and they don’t want a ton of bounces when they hit send (which risks losing your send privileges with pretty much high-volume email platform).

So they run all their emails through a service like this, and only send to the ones marked valid. This excludes a ton of emails that actually are valid, but failed the check (false negatives). But that’s ok because the emails were low-value to begin with.

If this sounds like a spammy operation… bingo. Technical email validation services are really only useful for people who are doing things like buying email lists from commercial providers, harvesting emails from sites like HN, or forcing people to enter an email address to do basic things with a free service.

Financial/fintech companies use services like these for fraud-detection on account opening. While validating an email is by no means and exhaustive and conclusive signal to classify a fraud/genuine user, verifying the validity of new customers's email addresses is a big help.

If you use Amazon SES and have a high bounce rate they will just block you. So, Eve could flood your registration with invalid emails that would cause bounces, that would stop all your emails from getting delivered. A DoS you can only recover from by switching to a different email provider

> Please hire me, SiriusXM.

Given their questionable business practices, their customer service dark patterns, their dated and awful UX, and their inevitable demise to much more popular streaming services, you’d be best to stay far away.

The service I work on emails users(B) after their email address has been input by another user(A) of our service. This would allow us to check that the email is reachable before we attempt to send the email. If it is not we can ask user(A) to check before they proceed.

I sometimes use it for sales. Looking up a company on LinkedIn, then finding the name of a person I want to each our to but am not sure about the email. Then I could try the classic first name.last name @ domain to see if it’s worth sending an email

I use to have a active product DearEle.com an email reminder service. There was a feature to cc everyone in email, which is used by spammers to send junk products to everyone. The source emails were all fake. Email check prevent fake emails.

> Please hire me, SiriusXM.

Honestly not where I thought that rant was heading ;)

I would love to clean up my addressbook removing no longer valid email addresses for contacts.

I’m tempted to add a spam detector rule that runs all From addresses through this.

Marketing?

It has honeypot detection. It's built for spamming people. There's literally zero reason to avoid honeypots otherwise

If you're asking for an email address in exchange for some piece of content (e.g. a soft paywall), I find that it's reasonably sensible to filter out the absolute spammiest-looking of email addresses in order to collect more real email addresses and prevent people just rolling their face across the keyboard and calling it a day. (It can also help with bots a little bit, although most bots are smart enough to use <random firstname>.<random lastname>@gmail.com or something). The best way to do this is obviously double opt-in, i.e. actually emailing the address in question. Most businesses believe (probably accurately; I don't have the stats) that this creates too much friction. I've used Sendgrid's email verification service in the past, and the actual scoring is basically garbage but if you set the threshold really low (e.g. reject all emails with a score between 0 and 0.1) then your precision is really good (almost every email address you reject is invalid, as measured by actually sending an email to them and the email hard-bouncing or being otherwise undeliverable). You let a decent number of bad emails through but it's an improvement over nothing.

The accepts_mail test seems flawed; a domain with no MX records can still accept mail (the spec requires an MTA to connect to the IP address in the A/AAAA record of the domain part of the mail address in this case).

All MTAs that I’m aware of support this, and it’s moderately common on personal domains with a single self-hosted MX, rare as those are these days.

Interesting! I did not know this

For those wondering, this is actually specified in rfc5321 section 5:

  If an empty list of MXs is returned,
  the address is treated as if it was associated with an implicit MX
  RR, with a preference of 0, pointing to that host.

https://datatracker.ietf.org/doc/html/rfc5321#section-5

I think they copied the licenses paging from a carousel library Flickity, they haven't replaced the company name from Flickity to reacherhq.

[0]:https://help.reacher.email/reacher-licenses#31b18f7872fc4480...

[1]: https://flickity.metafizzy.co/

Fixed, thanks!

Except if you try this with any real volume to most hosts, they’ll block you. These same techniques are used to dictionary attack as well.

Also, just because I have a catch all on my domain really shouldn’t be justification for saying my email isn’t valid and is a good way to lose business.

> Also, just because I have a catch all on my domain really shouldn’t be justification for saying my email isn’t valid and is a good way to lose business.

Agreed, 100% of the e-mails I use to sign up for services go to a catch-all.

Interesting tool, but there are some really concerning dark antipatterns here that I really despise:

  Is the address provided by a known disposable email address provider?
  Is the email address bound to a known free email provider?
  Does email address under test hide a honeypot?

What are the legit use-cases for this? To be sure you can force spam on your users and identify them as ad-targets?

If I ban a user who disrupts the functioning of the site, I don't want then to be able to immediately recreate an account. If there is more friction to this process, I can hope they will lose interest soon enough. Sure they can create an infinite number of Gmail addresses, but it might take then more time.

RE: use case

In our SaaS we enforce slightly stronger limits for trial accounts who sign up from free/disposable emails. User is Gmail? Well, sorry, +XX to "spam score". They will probably use our system for spamming.

They even link honeypot to spamtrap.

https://en.wikipedia.org/wiki/Spamtrap

The SMTP way of checking if an email exists is on the wrong side of CANSPAM, beginning the sending process to check an address is specifically addressed. And this assumes you didn't systematically "guess" the address.

Interesting. So if they are doing this are they violating CANSPAM?

EDIT: Looks like they are indeed doing the SMTP method: https://github.com/reacherhq/check-if-email-exists/blob/a052...

I also found a similar, much bigger service here that appears to have been around for a while: https://emailverification.whoisxmlapi.com/api

It speaks volumes about the marketing industry and how readily ethics and compliance are accepted even by companies that theoretically face consequences (though CanSpam seems to be lacking in enforcement here).

There are products that definitely make it past the seed round and sometimes even as public companies before enforcement notice that their entire product runs afoul the law.

Where do you see this in the law? I just skimmed through it, and I'm not seeing where it's addressed?

Search for "initiate", "headers", "open mail relays"; In addition to the law the FCC has additional legal guidance available.

If you do this search you'll see that the text of the act doesn't support what smileysteve says. See my other comment https://news.ycombinator.com/item?id=27713089

CAN-SPAM regulates "sending electronic mail messages". Connecting to an SMTP server to ask it if an address exists doesn't sound like that to me, but IANAL.

majority of mail servers do not support VRFY command, that is why the generic method of checking mail box is trying to send message (via MAIL FROM + RCPT TO) and breaking the sending halfway through

Okay, but that still sounds to me like taking an overly technical view. I doubt the courts will consider it sending an email if an email isn't received.

The law defines the word "initiate".

The act uses defines the word "initiate" and the SMTP only allows "asking if an address exists" via initiating a send (and then dropping the connection before a message is sent).

The act does define the word initiate, but it defines it to mean what the person who originally sends a message does so they can exempt relays. It's not originating or transmitting a message if you break off the connection before a message is fully transmitted.

> The term "initiate", when used with respect to a commercial electronic mail message, means to originate or transmit such message or to procure the origination or transmission of such message, but shall not include actionsthat constitute routine conveyance of such message.

I also don't think (but with less certainty) that what isn't fully sent counts as a message, as the primary purpose is verifying if the address exists. Message is defined as

> any electronic mail message the primary purpose of which is the commercial advertisement or pro-motion of a commercial product or service

Can you point out where in CAN-SPAM checking an address is specifically addressed? I haven't heard of this and a quick perusal of CAN-SPAM doesn't turn this up anywhere

Its "is_valid_syntax" result seems to be taking shortcuts and defaulting to "false" for anything not common. Reality is much more complicated: https://stackoverflow.com/questions/2049502/what-characters-...

Checked out of curiosity: it tries to confirm email existence by initiating mail sending [1] (likely very unreliably, since basic anti-spam measures would reject it before checking whether an address exists), and while it lists existence of paid services as the motivation, those paid services also mention unreliability and don't mention their motivation.

Now I'm slightly worried that in addition to counting me as a robot and an attacker, online services will think that my email address does not exist.

[1] https://help.reacher.email/faq

It makes me uneasy that the SaaS Website has no Imprint even while it writes "Made in a small independent studio in Berlin 🇩🇪."

In Germany an Imprint for a paid service is mandatory and after the ToS it seems like this is a product from a company in France? (I believe there are similar laws in France?)

Author here. Yes the company is in France, and I'm currently writing those (called "CGV" and "Mention légales").

What's an imprint?

https://en.wikipedia.org/wiki/Impressum

> The Telemediengesetz (German meaning "Telemedia Act") requires that German websites disclose information about the publisher, including their name and address, telephone number or e-mail address, trade registry number, VAT number, and other information depending on the type of company.

The relevant German laws (§5 TMG and §55 RStV) are fairly vague, so lawyers recommend publishing an Impressum if your website contains any commercial content (for example, ad banners) or any journalistic content (for example, blog posts).

> Has this email been compromised in a data breach?

Eep. My email is listed half a dozen times in Have I Been Pwned records, but I use different passwords for every site, so this means nothing.

Here, let me simplify that code:

  def has_user_been_pwned(email):
      return True

There. It's nearly impossible to be on the Internet at all without having some account or another be involved in an exploit at some point. You could rename the endpoint `user_had_a_facebook_or_twitter_or_linked_account_or_has_a_credit_score()`. This is a worthless thing to query because it tells you absolutely nothing about the owner of the address.

I think it’s genius, but evil. Like you say, real email addresses have all been pwned so this is a way to test for bogus or typo’d email addresses.

What a way to ruin a wonderful thing! Abusing the haveibeenpawned service in this way has worried me enough that I’ve now gone and removed my data from the publicly searchable database. I’ll use the notification service instead.

In the context of this thing, it means it's an email address that has been used elsewhere?

That's what I would hypothesize as well. Inclusion in a leak by HIBP increases the confidence that it's a real address (but not the converse). Weighting is left as an exercise for the library consumer :)

It is a weird metric -- sure, inclusion in HIBP increases the chance that it is a real email, but it also drastically increases the chance that the person who's using the email address isn't the original owner. Signed, the twitch account that "I" created.

That would only be a problem if you didn't ultimately require email verification. At least to me, this seems like a tool to decide if you should send email verification or block the signup attempt, but I can see how some people might choose to use the information from this tool to allow verification-free account signup

It seems like lots of places will let you start using the service without actually waiting for a response to the verification email. If they would use "in HIBP" as a flag to indicate that they have to actually wait for the user to click the verification link, that would be pretty cool.

This is just a tool that can run several checks, HIBP is one of the things the tool can check. At this point, probably everyone that has used a given email address for a significant length of time is going to be somewhere on HIBP. An app developer who uses this tool to prevent registration from an email that hits on this single test is going to discover the folly of their decision pretty quickly.

Don’t blame the tool.

I assumed the intention behind using HIBP was to permit registration of an email address in the database without further checking.

On your site (https://reacher.email) it shows "Open-Source" next to the MIT logo. To any reasonable person, that means "it's licensed under the MIT license". Instead, it's licensed under the AGPL. It would be good if you changed it to remove the implication that it was MIT licensed.

Good catch; the author (amaury) is using my service Saasify (https://saasify.sh) to auto-generate the entire SaaS website so this was just an oversight.

Uh, what? "Open source" doesn't mean "MIT" any more than "vehicle" means "truck"…

I don't even think the OSI classifies AGPL as an Open Source license, does it. Open Source is Free Software, but that's because it can be relicensed to anything as long as its attribution requirements are held to. Free Software licenses are restrictive (to preserve the access of the user to the software they use.)

The OSI does count AGPL as Open Source: https://opensource.org/licenses/AGPL-3.0

"it can be relicensed to anything as long as its attribution requirements are held to" is not a requirement of Open Source: https://opensource.org/osd

> next to the MIT logo

I mean, it's a stock image of "open source". There's a CC on there too…

It thinks the email address I've used for more than 25 years is invalid. Great job.

There is really no point validating emails beyond checking there is an @ in the address. Send an email to verify. You can even have an address with no . if you own the tld. foobar@me is a valid email.

Incorrect, I tried sending a mail and it bounced.

It is a valid email if the owner of the me tld sets up an email address on it. I'm not sure if anyone has done it on a tld but I have seen websites which are on the tld with no sub domain.

> I have seen websites which are on the tld with no sub domain.

Do you have any example of that?

http://ai./

It should only be possible on ccTLDs, this is not possible on newer gTLDs due to ICANN rules and I think no classic gTLD has it.

See: https://stackoverflow.com/a/40358071/4418149

I tried this on my email address and it didn't work. SMTP error "permanent: 5.7.1 <gmail.com>: Helo command rejected: ACCESS DENIED. Your email was rejected because the sending mail server seems to be impersonating another mail server (gmail.com)"

I hope nobody uses this for anything serious. I run my own domain and use <category>-<service>@<mydomain> to have a unique email for everything I sign up to.

I have no email address that this counts as anything other than "risky".

If this opts me out of marketing mail then that's probably a good thing, but I hope nobody puts a password-reset or security/billing notifications behind it.

I’ve been doing the same thing for years and haven’t had any trouble except for Mailchimp. Their overly-clever validation decided mailchimp@example.com is a shared email account (it wasn’t going to be) and blocked me from using it. Their email support apologized but said they couldn’t fix the false positive, and that they hoped the email I used instead wasn’t reflective of my opinion: mailchimp-morons@example.com.

Do you have a personal set up for managing these emails and disabling the bad ones? or are you using something like 33mail? Just curious.

I do the same thing, I catch every mail my domain receives and send it to a catch-all inbox. When ever an e-mail is "compromised" or is being abused, I can just forward <abused-mail>@<domain> to null space.

Why would that even be a problem?

Would you mind sharing your experience on how well that has worked for you? Has the complexity of maintaining different addresses been a problem?

I ask because it is something I have always thought about, but I suppose I kept hoping a service would come along and magic the solution for me. Kudos on making it happen!

I'm not OP but I do something similar, which I can describe. I don't whitelist addresses, I have a domain with a catchall account. So I make up addresses as needed. When I want them to die, I add them to a ruleset on the server that punts them into the bit bucket.

So far it has been really great. Easy, effective.

Edit: Like the other reply you got, I use FastMail for this service.

Here’s a good guide on how to go about this :)

https://btmiller.com/2019/12/12/regain-control-over-your-inb...

Dito, have been doing the same with a selfhosted mailcow for years. Never had a problem :-) Lately I started switching over to account+labels@domain.tld style because of the automated organization so I don't need extra routing rules if I want to organize them.

Except for the sites that reject the + character in email. I curse those developers who do that and never go back to that site again.

I do something similar and also use FastMail. I use <site-name>@sites.<my-domain> for all site signups, eg news.ycombinator.com@sites.example.com

Not OP, but I just accept wildcard *@mydomain and give out a unique name for every business. Works very well and I blocked a few businesses by which do not allow for opt-out and/or shared my address with others.

This is easy to do with the Alias feature of FastMail.

Yeah I do the same thing with FastMail - its awesome.

Here is a recent story where this came in handy.

I recently had a spam phone call from someone fishing for personal information, using a 'survey' as cover. During the call I learned that they had my email address as 'ledger@xxxx.xxx'. This must have come from the Ledger data breach (https://www.ledger.com/message-ledgers-ceo-data-leak). This made the call even more nefarious than I originally thought... nothing I can do, they have that email address and my personal number. Just made me more aware of what is going on.

That’s terrifying.

There is a service for that: https://anonaddy.com/

I've used it briefly for testing purposes and I have no complaints about it, it delivered what I expected with no hiccups.

Adding another comparable offering is https://simplelogin.io and you can set a PGP key for forwarded emails.

I did it for ages and eventually stopped. It gets awkward when you have to deal with customer support people and I never caught any spammers via the method anyway. Difficulty wise it was trivial since all emails hit my main address.

When I can tell it'll be awkward, I just make up some letters on the spot like "gj5@mydomain.com". It's easy enough to look for To:gj5 in your horded mail to find out what business it was.

I've done this too before, weird thing to have to do but sometimes people just don't get it. Although, nine times out of ten I get asked if I work at that business because the first bit of my email address is their business name.

I use anonaddy for this. A generous free plan, really feasible paid plans, and is open source so you can self-host it as well.

I use <mynick>@<signupdomain>.<mydomain>

I just disabled “load remote content” in email clients, stops spam pretty reliably.

This looks fantastic --- can you share some tips of setting it up?

This is more or less how I did it:

https://pastebin.com/q0H02FaF

Somehow my domain that I've owned without interruption for ~20 years got on a list of throwaway email services.

Glad to see I'm not the only person who does that! Great way to catch those who share/sell your email and to set up filtering.

I did this for 3 years and did not find a single case of spammers using one of the emails. All spam was from the sites I signed up with. Email spam filters catch spam for you.

This isn’t just good against spam. If there’s a data breach on the site, it’s another layer of insulation against you and other accounts you own. It’s close to the equivalent of Apple allowing you to sign up to services using one of their anonymous emails — there’s clearly demand for people to want to keep their emails from being thrown around everywhere.

Wouldn't someone be able to reverse engineer the pattern? I assume everyone is doing some variation of <service@domain.tld> so someone can try to figure out your other email addresses for other sites. Although I don't know if that's worth the time investment.

Right. The method has it’s own flaws, but it’s still another layer of insulation. Someone getting your email off a large user data breach is less likely to pick out your name and attempt to reverse engineer that pattern specifically for you, unless it is a targeted attack against you. For most people, that’s a highly unlikely scenario

For the catch all email setups yes. Not with the way apple does it. They have specific mappings setup so you have no way of finding other addresses of the user since every apple user is behind the same domain and the emails are long/random.

> Great way to catch those who share/sell your email and to set up filtering.

Couldn’t the seller just remove the prefix from all emails before selling them?

Aside from the questionable aspects of this it doesn’t even understand some aspects of how email works. It requires MX records, but it’s fine to just have an A record and accept email there, I do that for one of my personal domains and this says it’s invalid, but nothing else has ever had a problem with it.

Back in my day, we used to just telnet into the mx server and RCPT TO

That's what this project does too: https://github.com/reacherhq/check-if-email-exists/blob/a052...

I fingered that they were doing this

And before that you could just `finger` someone

How I sent my first email in 1995! Nothing like being able to write messages from bill@microsoft.com.

My email address reachability is "unknown", its a fastmail hosted account. Quite a commonly used service.

Is an unknown classification supposed to be treated as "I don't know, probably safe" or "I don't know, probably don't accept it" ?

    {
      "input": "***redacted***",
      "is_reachable": "unknown",
      "misc": {
        "is_disposable": false,
        "is_role_account": false
      },
      "mx": {
        "accepts_mail": true,
        "records": [
          "in2-smtp.messagingengine.com.",
          "in1-smtp.messagingengine.com."
        ]
      },
      "smtp": {
        "error": {
          "type": "TimeoutError",
          "message": "future has timed out"
        }
      },
      "syntax": {
        "address": "***redacted***",
        "domain": "***redacted***",
        "is_valid_syntax": true,
        "username": "***redacted***"
      }
    }

I'm going to guess that fastmail has blocked you lol

I also get "unknown" for my Zoho Mail addresses; also a pretty popular provider.

    {
      "input": "***redacted***",
      "is_reachable": "unknown",
      "misc": {
        "is_disposable": false,
        "is_role_account": false
      },
      "mx": {
        "accepts_mail": true,
        "records": [
          "mx.zoho.com.",
          "mx2.zoho.com."
        ]
      },
      "smtp": {
        "error": {
          "type": "SmtpError",
          "message": "permanent: 5.7.1 Email cannot be delivered. Reason: Email detected as Spam by spam filters. "
        }
      },
      "syntax": {
        "address": "***redacted***",
        "domain": "***redacted***",
        "is_valid_syntax": true,
        "username": "***redacted***"
      }
    }

I have my email with Fastmail too and issuing a RCPT TO command via telnet returns the following:

> 451 4.7.1 <marcus@utf9k.net>: Recipient address rejected: Temporary deferral, try again soon

The library identifies itself to the mail server with a from address of "testing@example.com".

It's probably a good idea to use an email address you own as the from address if you want to use this in production, eg: "testing@mycorp.com", to avoid this grey-listing.

Indeed:

  {
    "input": "testing@example.com",
    "is_reachable": "unknown",
    ...
  }

I mean I get the TimeoutError on the demo page.

  "smtp": {
    "error": {
      "type": "SmtpError",
      "message": "permanent: The host name specified in HELO does not match IP address."
    }

their server is misconfigured

I use disposable emails all the time, since nowadays you can't get the "free" wi-fi from business without a freaking registration.

Me too, it classifies mailinator as risky. I use it everywhere.

I use the name of the company that offers the 'free' wi-fi - eg nothanks@mcdonalds.com or chairman@walmart.com etc. That way they get the bounce back on their own mail servers and they also rarely refuse to accept it as a valid address for some reason :)

(note I'm just using mcD & walmart as place-holder company names, have no idea if they operate their public wi-fi that way)

Good strategy, I'll start using it too

Similar from 2009:

How to check if an email address exists without sending an email? - https://news.ycombinator.com/item?id=436817 - Jan 2009 (6 comments)

Spamhaus successfully blocks connection attempts by their SaaS service for not identifying itself with a valid domain.

If I were to self-host this (for instance to validate order emails and catch typos on a moderately visited e-commerce website, in the order of hundreds per day), what are the odds that I'll be banned by the major email providers (gmail, hotmail and co.) for abusing their servers?

You'll get blocked by your hosting provider first. See a recent instance here: https://www.lowendtalk.com/discussion/comment/3237390/#Comme...

Although many will criticise the level of perfection of this service, it could definitely be useful to many others. What is more, it is laudable that it's open source, and I guess that will lead to lots of community-driven improvements over time.

>could definitely be useful to many others

Its not about how useful it is to others. Its how it makes the web worse for users when their perfectly valid email address gets rejected because the flawed library said it was fake.

> The details of this [reachability=]"unknown" case can be found in the smtp.error and mx.error fields.

Indeed they can, my mail server seems to block the service because it already appears on multiple spam lists.

I feel like this will get your IP on block lists really quickly.

This feels like a service that would be used by shoddy email marketers and spammers to reduce the number of bad emails they send, so that they can avoid being blocked. Their home page (https://reacher.email/) mentions lists uses like cleaning "large lists", which comes off to me as code for "send mail of dubious quality without tripping alarms".

FWIW, similar popular libraries:

1. https://github.com/jeronimofagundes/EmailValidator#available... (PHP)

2. https://github.com/ivolo/disposable-email-domains (Node)

Checking if an email address is in a data breach and checking the user can click an activation link is a good way to de-spam free services.

Most real humans have at least one address involved in a data breach, but most don't have access to hundreds of emails in a data breach. That means most people can only make use of the "one free ice cream per customer" deal once.

Pretty neat!

Why this is not a library instead of hosted api? Why do we need to run this as a service? does it come with its own DB & all?

it's both; the OSS library is usable freely and the hosted version is auto-generated by https://saasify.sh

> does it come with its own DB & all?

Also, there's no DB. Each verification is done in real-time.

Disclaimer: IANAL.

This is a particularly interesting use of AGPL because it appears to contain a RESTful HTTP server built-in.

To my knowledge, with the way AGPL works, there are some interesting wrinkles:

- It is only intended to “trigger” when distribution occurs under some legal copyright law definition of “distribution.”

- It allows commercial use of unmodified and modified instances of the licensed code, as long as you provide the modified code, just like GPL.

- Being a copyright license and not a contract (at least not intentionally,) it only is “viral” to derived works and not aggregate works. So, depending on what you define a “derived work” as, some interactions between AGPL and non-AGPL code may be kosher.

Where this gets interesting to me is wherever you draw the line for derived works. For example, Ghostscript’s developers have a page regarding this subject:

https://www.ghostscript.com/doc/current/Commprod.htm

Particularly:

> The application calls GPL Ghostscript in a way that allows an ordinary user to substitute another program for GPL Ghostscript. (Typically this requires use of a shell script or batch file, or a system call like "exec".) More precisely, if the user deletes from the computer system all the files in the GPL Ghostscript directories, and replaces the GPL Ghostscript executable with another program with the same name and conforming to the same documentation, the application will continue to work with it. One implication of this is that the GPL Ghostscript documentation must specify all properties of GPL Ghostscript on which the application relies; for example, if GPL Ghostscript has been modified by the addition of command line switches or language elements such as new operators, the documentation must describe any such additions that the application uses.

If your AGPL application exposes a trivial JSON API, could you not write another application that simply supports a compatible interface, have it take an endpoint URL at runtime, and then just setup the software on another server and point to it? Although your software could be non-AGPL and maybe even closed-source, it could in theory be swapped out for any compatible service, including a simple noop implementation.

Assuming the author(s) retain the copyright for all contributions so far, they are obviously able to use the program without worrying about said licensing restrictions. But if you flip it around and someone else also runs a SaaS where they distribute the source as per AGPL restrictions, they could then offer said services and presumably it would not be possible for AGPL to have “virility” to spread outwards further. I can’t think of any reason this scenario wouldn’t work the same if done on internal networks by a single entity.

There is perhaps no particular takeaway here. In fact, maybe this was even intended to be a potential use case. However, I worry that this loophole may not be being considered:

> If you want to use check-if-email-exists to develop commercial sites, tools, and applications, the Commercial License is the appropriate license. With this option, your source code is kept proprietary. Purchase an check-if-email-exists Commercial License at https://reacher.email/pricing.

While it is obviously true that directly integrating the library into an application would indeed constitute a derived work, I am skeptical, based on what I know, that using a fairly generic REST API would necessarily constitute this.

I’m always a fan of open source as a model for better software development, but I do think that one really needs to be careful that it’s actually what they want. AGPL is a very interesting beast and there seems to be a lot of subtleties with regards to its implications in edge cases.

FYI: the additional requirements of the AGPL over the GPL trigger on modification not on distribution:

  Notwithstanding any other provision of this License, if you modify the Program, your modified version must...

https://www.gnu.org/licenses/agpl-3.0.html

Though if we follow this logic to its conclusion then using and distributing a program that cracks a trial version of software doesn't shouldn't be a copyright violation.

That said I would be interested if anyone could clarify to what extent a copyright license has any legal power if you're not distributing anything.

Once again, not a lawyer, but... A crack or a keygen is in fact not illegal under traditional copyright law. That is illegal under the DMCA, at least in the U.S., as a tool meant to circumvent access control.

Ignoring whether the keygen/crack itself is illegal, redistributing it with a trial version could be. Aside copyright licenses, there’s sometimes clickwrap licenses that disallow you from redistributing the trial at all. On the other hand, I believe it is unclear if a copyright license itself (as opposed to a clickwrap agreement) can actually disallow distribution based on other things it is aggregated with. This isn’t a terribly big issue for AGPL and GPL because they explicitly limit their terms to not apply:

> A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an “aggregate” if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.

> to what extent a copyright license has any legal power if you're not distributing anything.

Simple: no license, no copy.

It doesn’t matter how many copies you make, you still need a license. The “defence” of “I didn’t agree to the license” is basically admitting knowing and wilful infringement.

That seems a weird interpretation because the very act of reading the published code (including its license) is an act of copying.

I don’t think the act of copying could be illegal since backups are a thing

Just curious has anyone ever turned signups around and asked for the person to send an email instead? Something like send an email to signup@someservice.com

Then send a follow up confirmation email, no captcha required.

I’ve been doing it recently for some of my clients

It depends really on how valuable your service is and how easy you can make it for them to send you an email , for example auto filling subject and body using the mailto query parameters , so that they just need to click the send button on their email app helps a lot.

It does reduce spam on contact forms , that’s for sure, but I don’t yet have enough data to say whether it hampers signups in a bad way.

My clients are pretty happy with this method tho , as it works fine for their domain and who they target on their landing pages.

Personally I kinda like this method of signup , at the same time I find it annoying for when I’m not signed into the email I want to use on the particular device I’m using , while I could still send the email from another device , it does remove the ease of having it auto filled for me.

But everything has pros and cons, And I kinda like the new upside down way at-least when I build them for the services I work on.

Also it has a few issues : While I’ve practically never faced this issue in real life yet , but I can think of someone trying it.

Is if they fake the MAILFROM header , I’ve got a few emails personally where they faked the mailfrom and mailto headers , unless you verify them with dkim they can still spam you , but it’s very rare and I haven’t seen any abuse of this method as of yet , however if more people start using it , I can see it happen.

GitHub issues like this one warm my heart:

https://github.com/reacherhq/check-if-email-exists/issues/91

Identifying something that needs doing, especially when you have no idea how to do it, is a bold skill.

Too often have I seen engineers be reluctant to open an issue because they don’t know how to implement it, technically. I still do it, myself. If you need it then you’ll find a way.

The converse is also true: losing focus by filing tasks and procrastinating on features because you know how to build them, not because you actually need them to move your business / project forward.

May valid and working email address comes back with: "is_reachable": "unknown"

If you want to know the "how?" as I did - code is here, specifically https://github.com/reacherhq/check-if-email-exists/blob/mast...

tl;dr, According to RFC 5321, `RCPT TO` command succeeds with 250 and 251. So email is valid if you get to this part of the protocol and receive the response.

Really wish there was a way to disable email & avoid being on spammer mail lists

how to fail at email sending and tarpits, in one easy codebase...

It does exist, I used it this morning!

I HATE you for exposing this: <<"is_disposable": true,>>

i hope nobody ever uses this project, lest it break the usefulness of mytrashmail.com

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