At 12:48 -0700 on 08/08/2008, ned+ietf-smtp(_at_)mrochek(_dot_)com wrote about
Re: 2821bis/ter and procedures (was: Re: retry question):
> John's example is actually a perfect illustration of the context for my
original question. The server in question was using 450 replies to RCPT in
order to get separate deliveries of the same message for recipients with
different content filter settings.
OK, I have to admit, that's not a case I've heard of before, and it makes this
quite a bit trickier than I first thought: A server deliberately using
temporary failures in order to force the client to split the message up.
(Recipient limits in general can have this effect, but this is not
normally the
intent of such settings.) As long the the number of possible content filter
settings is small (2) this actually works acceptably well, but the fact that N
separate policies among the recipients of a given message will require N-1
retries makes this impractical in situations with lots of possible filter
settings.
A possible solution would be to define an EHLO 220 reply that says
"Single RCPT-TOs ONLY" and blow off the sender if they try sending a
second RCPT-TO (by at least 450'ing the extra RCPT-TOs). I will not
suggest rejecting the DATA command although since that would prevent
relaying from MTAs that do not understand the 220 Requirement to
split Multi-Recipient messages into individual messages and keep
sending the messages as Multi-Recipient messages.