Typos are the primary motivator, true.

It's not side-stepping RFC2821 so much as it is working around the widespread switching off of VRFY support, which is a response to spammers abusing VRFY. Mail::CheckUser provides a mechanism that, by default, does not treat a full mailbox as a failure, and the docs suggest against treating a timeout as a failure. What I do in response to timeouts is explain to the user that his address could not be validated "due to temporary network congestion", and bother him to confirm that it's correct. After that, the SMTP server gets to cache and retry as necessary when it's time to actually send email.

I've yet to hear a complaint from a user with a valid email address which has been rejected by these kinds of checks. It's certainly possible that a user could happen along while his DNS administrator is experiencing a fit of incompetency and there are no MX records to be found -- frankly, I consider this to be in the "Not My Problem" category. I'm not aware of it happening yet on any of the sites I administer, but if it becomes a recurrent problem I suppose I'll have to deal with it somehow.

In reply to Re^9: Yet Another E-mail Validation Question by gloryhack
in thread Yet Another E-mail Validation Question by tanger

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