I understand that there is no complete regex to actually determine whether an e-mail address is valid/deliverable.

What's the obsession of people to check for valid email syntax with a regular expression? Checking whether a given email address has a valid syntax (which isn't the same as being deliverable) isn't too hard - it takes a bit of grunt work, but the grammar of RFC (2)822 is pretty straightforward. There are even some CPAN modules out there that do this.

But doing it with a regex is pretty hard. Yet, people seldomly ask how to check whether an email address is valid - instead, most of them insist on a regex.