Can LMTP reject mail rather than discard after accepting?
In a recent post on Mailman-Users, Richard Damon points out (not the first time or the only person to notice) that it would be really nice if Mailman could be queried by the MTA, which could be told to reject at the SMTP level. This would require at a minimum milter (Postfix, Sendmail) and Exim support, which IMO would be a maintenance burden. I wonder if we could use appropriate status codes in the LMTP protocol to do the same job in a unified way (since all reasonable MTAs speak LMTP pretty well).
Probably related: #14 (closed), #69 (closed), #90