in reply to Re^3: Yet Another E-mail Validation Question
in thread Yet Another E-mail Validation Question

My point, and maybe i didn't communicate it well, was what problem does checking that the mail server exists solve? A nice good user wont enter fake mail servers, and a mean user trying to abuse it will obviously choose a domain that has a mail server active.

So my real question is "what case did i miss?" Is there some other possiblity that I'm missing in which a nice user somehow accidentaly types in a bad domain name but doesn't mean to? And why is checking the domain in that case better than two email boxes or sending a test message?


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Eric Hodges
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Re^5: Yet Another E-mail Validation Question
by gloryhack (Deacon) on Apr 22, 2005 at 05:06 UTC
    Oh! In that case... yes, users do often enter their email addresses incorrectly into forms. Others, for whatever reason, will trust you with their credit cards, but not with their email addresses. Odd, but it happens.

    If you're doing e-commerce, you want to ensure that you can, in fact, contact the customer if there's a problem with the order (or payment for it). If you're running a mailing list, especially if it's a large one (as promotional lists often are), it's just good practice to minimize bounces. Some mail system administrators get grumpy if you fling too many invalid addresses at their servers -- who could blame them? It's sometimes hard to tell innocent errors from dictionary-attack spamming or joe-jobbing.

[reply]
      Some mail system administrators get grumpy if you fling too many invalid addresses at their servers -- who could blame them?

      And checking for whether the mail server exists prevents this? I'd be surprised.

      Trying to send out an email to a host for which there isn't an MX record won't anger any postmaster (except perhaps your own), as no mail will get delivered. And if it's going to hammer a DNS server, enable caching. ;-)

[reply]
        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.

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