Robert A. Rosenberg wrote:
Not relevant since the scenario we are talking about is not the MUA
sending a 150 to the MTA but the MTA sending the 150 to the MUA (so as
to restart the Time-Out clock and keep the session Open/Alive).
In general, an SMTP server cannot know whether the SMTP client is MS
Outlook or Sendmail.
The whole business of sending back part of a multiline reply to trick
the client into extending its timeout seems smelly to me. In today's
environment when you might have hostile servers trying to tarpit
clients, I can see a client not wanting to extend its timeout just
because a network packets are trickling in. The proper way to do
in-progress reply codes is to make an in-progress ESMTP extension that
the server advertises and the client asks for.