in reply to Re^2: Yet Another E-mail Validation Question
in thread Yet Another E-mail Validation Question

Checking that the domain is valid, and, to the extent possible, that the email address exists, saves network and server resources that would be otherwise be consumed by rejections from the local SMTP server and bounces from remote SMTP servers.

Of course anyone who's of a mind to be a pest can sign a disliked person up for a bajillion mailing lists -- that's why a well-designed list server will provide for double opt-in to confirm subscriptions. That's not the problem we're trying to solve here, though, is it?

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Re^4: Yet Another E-mail Validation Question
by eric256 (Parson) on Apr 21, 2005 at 23:04 UTC

    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?


    ___________
    Eric Hodges
[reply]
      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. ;-)

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