No, an MX lookup doesn't prevent that -- but the SMTP checks that Mail::CheckUser provides often can. Mail::CheckUser has the option to do an SMTP conversation with the MX, doing HELO, MAIL FROM, RCPT TO, response check, and QUIT. If there's no MX, or the MX tells you that it won't accept mail from you or for that user, you're better off knowing early enough in the process that the user can correct the problem.

I can see no good reason to task my SMTP server with caching, retrying, and ultimately returning undeliverable messages whose addresses could have been corrected by the user very early in the process.

Again, in e-commerce, it's important to ensure that users who are expecting email actually receive it. The alternatives are expensive: telephone calls and/or lost customers. It's important, I think, to support those lousy typists with valid credit cards.

In reply to Re^7: Yet Another E-mail Validation Question by gloryhack
in thread Yet Another E-mail Validation Question by tanger

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