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Comment by dharmab | Hacker News Reader

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).

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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.

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.

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!

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.

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