SMTP session. I'm hearing a reasonably strong consensus that it is now
acceptable -- and possibly essential -- to do some serious processing before
responding.
Yes, definitely. One of the reasons people hate my favorite MTA,
qmail, is that it implemented the advice to respond as fast as
possible, queued incoming mail immediately, and deferred all
rejections until later, even invalid mailboxes. I, and most other
qmail admins, have replaced the standard SMTP daemon with one that
does a lot more, in my case including DCC lookups and spamassassin, as
well as most invalid user rejections, before responding to the client.
R's,
John