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Posted by "Michael Sims" on 09/21/05 22:31
Philip Hallstrom wrote:
>>> but you could do what you want to do. however, it's going to be
>>> painful if you want it to match the rfc spec...
>>
>> Really? Why does it need to be painful? I just need to do a
>> 'EHLO', 'Mail From:' and 'RCPT to:' and 'QUIT'. It's not going to
>> actually send an email. Seems simple to me. Maybe there's something
>> else in the spec that I don't see?
>
> Some mail servers can be configured to not reject the email until the
> end of DATA. I know you can do this in postfix.
>
> Although if the user is invalid, why you'd wait I don't know, but it
> is possible.
Additionally, some mail servers unconditionally accept mail addressed to ANY
username at their domain, whether that user actually exists or not. This is very
bad practice, because it usually means the accepting MTA is a "dumb" host that has
to forward all incoming mail to an internal mail server which knows which accounts
exist, and if that server ends up rejecting the message, the "dumb" MTA creates a
DSN and sends it back to the envelope sender (which is quite often forged). This
causes the so-called "backscatter" which results in innocent people getting bounces
for messages they didn't send. Nevertheless, lots of mail servers are configured
this way, so you cannot simply assume that an account is real just because you
didn't get a 5xx on RCPT TO.
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