On Fri, Oct 27, 2023 at 08:20:37AM +0000, Exim Bugzilla via Exim-dev wrote:
> I am opening the bug so late because it is not easy to say anything
> about this problem except that the Exim disconnects after the end of
> DATA (.) for some(!) mails. It is independent of the recipient of the
> mail. Some mails to the recipient work, others don't, but the mail
> that doesn't work fails every time I try to send it. The problem
> occurs both with mails to be stored locally and with mails to be
> forwarded.
The most plausible scenario here is that this is a combination of
PIPELINING and a potential middle-box in front of Exim that closes the
connection on QUIT, but fails to take PIPELINING into account.
With PIPELINING, the SMTP client send ".<CRLF>QUIT<CRLF>" together in
one packet, and then waits for the "." response. If some firewall
shuts down the connection on encountering the incoming packet, the
client never gets the "." response.
I can't rule out an issue inside Exim, but it seems "unlikely", since
such an issue would have broadly visible impact, breakign mail delivery
for a large fraction of deployments.
If you configure this particular Exim to not advertise "PIPELINING",
that could help.
You could also temporarily as a sanity check, temporary replace it
with Postfix, and perhaps observe the same behaviour, which would
additional evidence of a middlebox as the culprit.
--
Viktor.
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