[thedufer]

> But you'll never get a test that can prevent errors like [e-mail], [e-mail], [e-mail] etc. So is it really worth doing any checks at all?

You can do quite well at this, if you're willing to not restrict yourself to regexes and commit to some amount of hackery. One system I worked on used a simple regex (just what is described here IIRC - assert the existence of an @ sign), plus did an MX check on the domain, plus warned (not errored) if the domain was within 1 or 2 Levenshtein distance of any of a list of most common email domains (yahoo, gmail, etc). Statistically it seems like we saved people a lot of grief with this simple filtering.