Toot

Written by gjm on 2024-09-27 at 00:40

Clever internet people! I have a weird network problem.

My local machine is a Linux box. It runs Exim, a mail transport agent. When I send an email, my mail user agent talks to Exim, and Exim passes the message on via SMTP to one of two remote smarthosts for further delivery.

For one of those two, but not the other, something times out when trying to make the SMTP connection. The message in the Exim logs is "SMTP timeout after initial connection" but I am not certain there has actually been an "initial connection" in any useful sense.

When it's trying to deliver such a message, netstat shows the connection to the relevant server as in state SYN_SENT.

Usually I think this would indicate some rather low-level network problem, like a broken firewall rule.

BUT

1. If I try to make a connection (from the same local machine) to the same server using smtplib in Python, it connects without problems! (And I can successfully send mail that way.)

2. Between the last time this all worked without problems and now, I have not knowingly changed anything in my configuration.

Yes, I have tried turning it off and then on again.

Anyone got any idea what might be happening?

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