[kidsil]

Gmail gives you another option - separate using dots.

[e-mail]

The number of options is of course limited but it's still recognized as a separate address while still coming into the same inbox

[dsl]

I've built a few registration systems and always normalize email addresses (remove local part, de-dot gmail addresses) at signup and login.

It helps users who keep trying [e-mail] when they signed up with [e-mail]. Also is pretty good at preventing mass signups using tricks like this.

[jake_the_third]

How do you know where the local part starts? Google uses '+' but nothing stops you from using '-' as a delimiter if you're running your own servers.

Also, how do you deal with spam filters that are designed to spam anything without a local part? Or is this only done to "well-known" domains like gmail.com?

[apexalpha]

>if you're running your own servers.

This is enough of a threshold probably.

[apexalpha]

Actually [e-mail] would work too, since it fully ignores dots. So the options are just as (not) limited as anything a + can add.