detecting bounced mails

Sorry..the topic does not fit here. But wanted to know, how can we check validity of an email id "in advance" so that we can skip "bounce".

Thanks!
Rajiv

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There are theorethical ways using SMTP's VRFY command, however it has never been implemented at all systems, and modern environment of firewalls just simply doesn't allow it to work.

The only thing you *can* verify is to look for the domain part in the address from the DNS. At first query for MX record(s), and if *not* found any, then query for A record(s). If you encounter CNAME, do resolve it couple times towards MX or A.

If you find neither MX, nor A, then the DOMAIN part is non-routable in the internet, but nothing can be said about the left side of the @-character (the LOCAL part).

If you have a RFC-821 statemachine scanner to recognize the address syntax and accept only LOCAL@DOMAIN form (not @GW1,@GW2:LOCL@DOM), plus do that MX/A lookup, you should pretty much be done.

It will trap honest mistakes - usually.

I have code to do this type of analysis at my ZMailer, works fine.

/Matti Aarnio
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You can't. Only think you can check is a valid domain that will in theory accept mail, no way to check if it really dilivers.

Igmar

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