[DanBlake]

I disagree. While n@ai might be a technically valid email, its such a extreme edge case ( maybe 1 out of 1,000,000 people have a email like this) that its worth denying that person registration to keep the likely thousands of erroneous emails from being entered incorrectly and the time that goes into correcting them. Same thing goes for addresses like "<>;@\'`{}|.a"@παράδειγμα.δοκιμή

Honestly, if you decide to use a email like n@ai you already know what to expect. Most services wont let you sign up, And even if they do most will likely incur errors in the application when you attempt to do things.

In reality, while it may be 'in spec' to use such a email, we can all hope that edge cases that allow it are changed and the legacy 'rules' that allowed it in the first place phased out completely.

So, in practice in the 'real world'- n@ai is not a valid email address and never will be. If I create a web application you can bet your bottom dollar I wont allow it and I will create less work for myself by doing so.

[ubernostrum]

Probably also will "fail" on most of the valid-according-to-the-RFCs addresses in this thread:

https://twitter.com/errbufferoverfl/status/10197667755614453...

And I don't mind at all. Many of the things you can technically do in an email address are needless complexity that shouldn't be encouraged.

[jeroenhd]

So people with an exotic email address can't use your service because you don't think their email is valid? The reason you don't see those exotic addresses are mostly because of bad programs not knowing how email works.

This reminds me of that story of a Chinese man unable to get registered at the bank because the computer systems don't have a character required to write his name.

Sure, "it only affects a small amount of people", but it shouldn't be that hard to just flag strange but valid emails with "your email looks strange, check it again and tick this box if you're 100% sure you typed it right" instead of outright refusing to work. The check box doesn't even need to be interpreted server side, this can be done in one or two lines of javascript.

[saagarjha]

It might be worthwhile presenting a warning to the user, with an option to forcefully override it.

[DanBlake]

So, thats more code you want me to write, to support how many total potential users on the planet? I'm good. They knew what they signed up for when they chose to use an email like that and I am sure every single one of them has another email they use for this case.

In fact, I bet many of them are so frustrated with the errors of nothing working that they dont even attempt to sign up for things with the email most times.