David wrote:
I would really like to see other MTA software (qmail, Postfix, Exim)
implement "real-time" filtering during the SMTP conversation. As far
as I know, Sendmail is the only MTA that does this currently.
Mailshield provides inline "real-time" filtering which can take effect
at any RFC821 "step" of the conversation - connect, HELO, MAIL FROM,
RCPT TO or DATA. [Mailshield is from Lyris, I made the designer build
it that way ;-)]
We've deliberately altered this so almost all of our rejections occur
after the DATA so we can get full copies of everything we block. The
only exception is relay attempts - we block those at RCPT TO time.
Mailshield isn't a true MTA - it's more of a RFC821 packet filter,
"front ending" a "real" MTA. In our case, the back end is sendmail.
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