Does anybody see a need/desire/etc for an ESMTP option to advertise
this limit, so the upstream end can avoid sending a RCPT TO: that
will just get 452'd anyhow?
Straw man proposal:
250-MAXRECIP nnn to state that more than nnn receipts will not be accepted.
FWIW, Zmailer says X-RCPTLIMIT n for some n, but I don't know what its
SMTP response is after n RCPT TO commands.
It -is- protocol bloat, and with ESMTP pipelining the extra commands
aren't terribly expensive, so it sounds marginal.