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Comment by flurdy | Hacker News Reader

> So if you’re enforcing unique email addresses, or using email addresses as a user identifier, you need to be aware of this and you probably need to strip all dot characters from the local-part, along with + and any text after it, before doing your uniqueness check. Currently django-registration doesn’t do this, but I have plans to add it in the 3.x series.

Sorry what? That seems pretty unneccessary. A third party system to dictate how a third party system handles it local alias system for emails? I can't see any benefit to that.

Whether a mail server handles '+' in a standard way is not guaranteed, and surely it is up to the user how they use that feature if enabled.

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Absolutely this. It's not even a standards issue, for the outside world they're completely different email addresses. The fact that they happen to land on the same inbox for some providers is unrelated, it's just how that particular provider decided to handle all your different email accounts.

Yes! And if you have your own domain, you can just setup a *@example.com to be your one email address. And then you can give a different email address out anyway even without needing to go +. As you said each system can treat it differently.

Agreed.

From RFC 2822: "The local-part portion is a domain dependent string."

Headaches await you if your code is making a lot of assumptions about how the originating domain manages that local-part portion.

Apple ID's make assumptions (they strip out the + and everything after it) and it's made it a nightmare to use iTunes Connect. Their multiple account support is still terrible so it's easiest to have an Apple ID per iTunes Connect account. Now I need to setup actual aliases in my GSuite account...

Stripping out things past the + will also break things for users that intentionally are creating more than one signup. This seems like a really bad idea.

That's the entire point, no?

Why do you want to detect the difference between a user signing up with one email account twice or two different accounts? It's folly to try to detect this in this manner and you will only piss off regular users.

The service that's trying to strip the +'s are trying to prevent users from using their (usually free) service in a way that will cost them more money, but never convert to and profit.

i understand why they do it, but i can't condone it off course.

The service should just allow it, and make sure the appropriated subscribing fee.

> The service that's trying to strip the +'s are trying to prevent users from using their (usually free) service in a way that will cost them more money, but never convert to and profit.

I can always create multiple email accounts, you know. So I don't see how spending development efforts to parse and detect + and . is effective.

It's a pointless and stupid point.

It is extremely easy to setup extra email accounts, so preventing people from doing so with slightly less work is pointless.

It is stupid because it could prevent someone from using their real, valid email address because it matches another, different, valid email address.

Agree. You're going to regret doing this when you try to test it yourself, with your own Gmail (or GSuite) account.

Agreed. The + thing probably is "only" unfriendly to powerusers, but stripping dots can easily get in the way. Several of my e-mail addresses have "duplicates" that just differ in a dot and are owned by entirely different people.

> so it’s impossible without doing DNS lookups to figure out whether someone’s mail provider actually thinks johndoe and john.doe are distinct.

The author has announced they believe them to intentionally indistinct and has announce an intent to break handling for any mail servers that consider them unique. All on account of gmail ignoring them?

This coupled with their author's intent around + makes me loathe this behavior.

I was with him most of the way, but the advice about emails seems very user hostile to me.

It is worse than unnecessary. If people start irrationally doing things like recognizing the '+' then that creates facts on the ground which rational reasons for others to have to recognize the '+' -- except nobody really knows why anyone is doing it or what semantics anyone else is using. Thus the whole thing evolves into mess.

So please don't do that. Respect the bytes that be!

yeah, I actually use google's plus-email features to help me generate test accounts on some sites or to attribute mail spam to other sites.

If you don't do this your system may allow users to sign up for multiple accounts and double-dip on signup benefits, free trials and other "one per account" features. (Barring additional controls, of course).

Well, that's always a risk. The thing this guards against is someone accidentally creating two accounts with variations on the same address and being very confused.

i recall Amazon did something quite amazing, which is to suggest to the user who signed up twice whether an existing account is the same. but only after they've purchased!

Or they could just sign up at one of the numerous free email providers with a different username. Stripping the + suffixes is only providing one thing - pain for the users that want to use it.

The author suggests stripping the part before doing the uniqueness check. This does not mean that the username (email address in this case) would not be allowed.

It would for the second user whose address resolves to the same result from the “uniqueness” check.

I wish this would happen. There's a "rocket surgeon" on the East Coast who has (tried) to sign up for Facebook, Twitter, Steam, and a bunch of sleazy 'message gurlz now' apps using my Gmail address without the period.

Obviously it never works, as I get the "I see you're trying to create a new account" email, but one of these days he's going to figure out a way to take over one of those accounts and then I'll really be fked.

I have a similar problem with someone who keeps (hopefully accidentally) putting my landline number into Facebook, then I get a call with a recording asking me to press some number to verify my Facebook account.

I don’t understand your complaint. Google resolves the addresses john.smith@gmail.com and johnsmith@gmail.com to the same account, which you control.

(1.) What are you imagining is the attack vector exactly?

(2.) Are you asserting that all website owners should build to Google’s (non-standard) behavior?

I'm curious as to who would use a service someone else is using, sharing their email but with a local addition?

Can me and my wife both sign up to HN and use my email but hers be josh+swife@joshmanders.com and mine be josh@joshmanders.com?

That's a strange usecase, isn't it?

gmail makes josh@... and josh+swife@... resolve to the same thing, but there is no guarantee that all other email services behave like that. For all you know, there is an email service that lets you register an email like that, so you have 2 users now whose email is: john+smith@... and john+brown@...

It's way easier to write a script to generate thousands of variations on the same email address than to sign up for a thousand different accounts. I've actually been bitten by this bug before... or rather, my company was bitten by an affiliate who neglected to sanitize their emails this way and someone was able to create thousands of gift cards in our system.

Having said that, in development, it's super nice to be able to create addresses with +'s in them.

What you say is not untrue, but it's still bad advice to do it -- a security red herring. First of all, you don't know that 100% of mail servers ignore characters after the +, so you can't safely strip those characters or you might not end up with a usable email address. That goes double for stripping the dots/periods, which gmail ignores but many other mail servers do not.

On top of that, it's just as easy to set up a catchall email address -- an email box that accepts all mail for a domain, literally anything@mydomain.com. So a malicious actor could sidestep this security attempt with minimal effort, but it still inconveniences legitimate users despite being worthless from a security perspective.

True, true. As I mentioned below, in my case, it was even usernames, just entering you email for a free gift card. The attacker actually used dots with a gmail address.

There are soooo many ways to easily game the email side of it that you would be better off using other means of detecting uniqueness (rate limit per IP address, rate limit per hash of IP address and user-agent)

>It's way easier to write a script to generate thousands of variations on the same email address than to sign up for a thousand different accounts.

It's just as easy to write a script to use ephemeral hosts that you don't need to sign up for. Things like Mailinator.

All it does is irritate people like me who use +words as prefilters for email (and to see which companies are selling my email/user data).

Fair enough! In my case it wasn't actually usernames, just entering an email address through a phone company for a free gift card from my old company so yeah, my point is moot.

That's all fine, but except in pretty specific circumstances you're going to have valid reasons to want multiple accounts for a single email address. Kind of a crazy scale issue, but one example is wanting your AWS Account to be separate from your Amazon Retail account, even though they use the same underlying account store it's a good idea to use separate accounts even if they're tied to the same email.

This is true. I know someone who says she's been doing the Hulu free month thing for a couple of years, and does it for other services as well.

It's all too much for me to keep track of, but for some people it's no big deal to create new e-mail addresses every month.

If you as a service provider can't accept that you shouldn't be offering those free trials / benefits at all. This isn't an issue.

You’re gonna be sad to know that mailinator[1] and it’s 100s of domain aliases exist.

You’re fighting the wrong battle.

[1] https://www.mailinator.com/

Some places check for these types of services though

They do, but they're not very effective. They might have an up-to-date list of domains belonging to the big services (i.e. Mailinator), but you can always just google "Disposable e-mail", open the 10th page and pick the first one, and it's pretty much always guaranteed to work.

I beg to differ. I use this blacklist and not much gets by. Anything that does, I blacklist manually.

https://github.com/martenson/disposable-email-domains/blob/m...

A lot of sites I've come across lately are going back to the old-school way of only whitelisting email addresses from .edu domains or ISP accounts ("@comcast.net").

That's an absolutely ridiculous idea and a good way to destroy the amount of users you're getting. Do you whitelist Gmail? Then it's piss simple to sign up to multiple accounts. Do you not? Good luck a massive portion of the internet to sign up...

I don't want the sort of users who are signing up to perform financial transactions using services like mailinator and guerrillamail. It's always fraudulent.

Gmail itself is allowed, but the addresses are normalized. I'm well aware of its potential for abuse.

I think what the parent meant was that creating multiple gmail accounts is also piss-simple.

I personally own over 100 from a couple years back when recapta was easily automateable and the phone-number requirement wasn't there.

I have infinity. I use Gmail for business with a catchall rule that forwards to the one address in my domain.

I have an email address for every site I sign up for.

Helps you figure out who sells your email.

How do you handle this? Or do you not?

I guess you could do a DNS lookup of the mail exchange records and see if it points back to gmail and compile a list of domains to allow one account from... but then that would break many companies emails. That’s no fun.

I use Fastmail in exactly the same manner (catch-all, I use "yourdomain.example@mydomain.example" as the email address for signups). Also, anyone could put a cheap domain name on Migadu with a catch-all for this purpose.

Services need a better way to figure out fraudulent or abusive behaviour than guessing based on the email account's domain name.

> only whitelisting email addresses from .edu domains or ISP accounts ("@comcast.net").

I haven't seen ISPs give out emails addresses like that in years (I now my last couple of ISPs have no such thing).

So you're basically limiting yourself to people from universities, or who've had an old-school ISP for a while.

I've yet to see a fixed ISP that doesn't give out email addresses; though I very rarely meet anybody who used them as anything other than a fallback for their webmail addresses.

Mobile carriers even still seem to, though they are optional and require an additional setup step.

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