[ubernostrum]

Conforming with the standard is not "effectively free".

The only way to _really_ validate an email address is to try to send mail to it. But that has non-zero cost (depending on how often you have to do it, what the odds are that you'll end up on a spam blacklist for no good reason, etc., etc.).

The alternative is to use purely server-side validation routines. But these become more and more expensive as you progress through less common edge cases (e.g., regular expressions are not capable of detecting every valid address). So most people, sooner or later, make a trade-off, favoring some more common subset of cases over some less common subset.

If anything, we should be arguing over what constitutes an acceptable place to make that trade-off. Should embedded comments be supported? What about bang paths?

[ars]

If you are not going to email to it, why bother asking/storing it?

[ubernostrum]

Maybe you don't need to send email right away, but want to store the address in case you need to get in touch with the user?

Sending one email per signup can be problematic depending on the volume of signups. Sending email only when absolutely necessary can help with that.

[ankhmoop]

If you really care, use a real standards-comformant address parser, most languages have at least one -- Java does. Otherwise you're just wasting your time, and the time of any users you hose with your amateur-hour validation.