I've been using Mail::CheckUser for quite a while, and haven't had any complaints. It provides regex address syntax checking, with optional DNS and/or SMTP checks, and so far I haven't heard a complaint from a user that his valid email address has been rejected.

I usually just warn the user that the check could take up to 30 seconds, and do the full DNS and SMTP checks while the poor slob waits around. In cases where the wait is considered unacceptable, I just do the DNS checks when the form is submitted (catching things like "aol.cmo"), and then weed the mailing list with the SMTP checks later. qmail and postfix are the main culprits in later bounces, but they're fewer and further between than they would be if we just blindly mailed to all of the syntactically valid addresses.

Shouldn't your SMTP server be retrying on full mailboxes and other temporary (4xx) errors?

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

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