[RFCI-Discuss] acceptable filtering of RFC2142 mailboxes?

[James Ralston]

Certain RFC2142 mailboxes at our site (e.g., postmaster, abuse)
receive lots of spam.

Unfortunately, due to the relevant RFCs and the role these mailboxes
play, we must accept (virtually) all mail to these mailboxes.

This is problematic in terms of handling spam.  For example, if the
recipients for a single message are all non-RFC2142 recipients, and
the tests our MX server performs indicate a high probability of spam,
we would reject the message during the SMTP dialog.  But if just one
of the recipients is an RFC2142 recipient, we *must* accept the
message, even if we are virtually certain it is spam.

In essence, including an RFC2142 recipient "auto-whitelists" the
message.  We wish to prevent spammers from taking advantage of this.

Therefore, we are thinking of implementing a restriction that a
message must either have *all* RFC2142 recipients, or not have *any*
RFC2142 recipients.  If your message includes both RFC2142 and
non-RFC2142 recipients, you will receive the following error after
sending the "." to close the "DATA" command:

550 5.7.1 mixing RFC2142 recipients and non-RFC2142 recipients not permitted; please resend to recipients individually

My read of the rfc-ignorant abuse/postmaster guidelines is that
filtering on this basis would *not* be grounds for being listed.

Agreement/disagreement?

-- 
James Ralston, Information Technology
Software Engineering Institute
Carnegie Mellon University, Pittsburgh, PA, USA