On Sat, Feb 27, 2021 at 10:31:50PM +0100, Heiko Schlittermann via Exim-users wrote:
> I assume, that a connection coming *from* outlook to you. They (outlook)
> seem to have the bad habit to forcefully tear down the connection as
> soon as they received your "250 OK". They don't send a QUIT, nor do they
> perform a regular SSH "good bye" handshake. They just behave rude.
If this is indeed a connection closed after message delivery, there are
a few possibilities.
1. ESMTP PIPELINING was not used to pipeline "DOT" and "QUIT",
the server sends QUIT separately, but does not wait for a
response and hangs up.
Not waiting for a QUIT response is not uncommon, but PIPELINING
typically hides this because the sender will of course wait for
the DOT response, and it will typically be sent together with
the QUIT response, when the commands were pipelined.
2. Exim is sending a TLS close_notify alert when closing the write
side of its SSL connection, and reporting any I/O errors that
may occur when doing that. Here, it may be reasonable to not
report these. SMTP is not a protocol where data truncation
is a concern, SMTP framing takes care of that above the TLS
layer.
3. The client does not even send QUIT, and just closes the channel,
but here, I would not expect the server to send any SMTP
response, so if it is still writing something, it is probably
again the TLS close_notify (as in 2 above).
Perhaps more, but these are the ones that come to mind.
--
Viktor.
