REJECT-ON-SMTP-DATA (Re: Mail Server best practices - was: Pandora's Box of new TLDs)

Jean-François Mezei jfmezei at
Sat Jul 5 08:52:43 UTC 2008

one note about whether to filter at receiving SMTP server or later.

The receiving SMTP server is the one that has the conversation with the

Rejecting mail from servers having an un-backtranslatable IP is best
done right away by the receiving server right after the HELO command by
issuing error message about the IP being unbacktranslatable. Reduces the

later on (for instance at the client level), you need to parse the
RFC822 text header and there are some bits that are missing, notably the
RCPT TO: commands. This is especially true when the "TO" in the 822
header is faked.

Blocking messages as early as possible also greatly reduces the load on
your system, disk storage requirements etc.

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