At 09:45 -0700 on 04/30/2007, ned+ietf-smtp(_at_)mrochek(_dot_)com wrote about
Re: "for" clause on Received: header field:
The problem I see with the matching approach, aside from the obious overhead,
is while you can assume that a successful match to, say, a To: field means it
is OK to expose that recipient address in a for clause, not finding
any matches
doesn't mean the address has bcc semantics. So you end up presenting
the subset
of the active recipient list that happen not to have been transformed by
forwarding/routing activites in ways that prevent matching. The result makes
for clause disppear in prcecisely the cases where it is most useful for
debugging purposes: When transformation of the recipient addresses by
forwarding/routing has led to a mismatch between what's in the header and
what's in the envelope.
The solution to the matching issue is simple. If you are the ultimate
receiver domain (ie: Example.com for mail addressed to
*(_at_)example(_dot_)com), just clone the message so there is a separate copy
for each Rcpt-To address and place the appropriate address into the
for clause of each cloned message - IOW: Act as a SMTP Server that is
designed to not group multiple Rcpt-To commands into an outgoing
email message even though the Mail-To's point at the same MX Server.