https://bugs.exim.org/show_bug.cgi?id=3138
Bug ID: 3138
Summary: Connection reuse does not take TCP port + wrong port
logged
Product: Exim
Version: 4.97
Hardware: x86
OS: Linux
Status: NEW
Severity: bug
Priority: medium
Component: Unfiled
Assignee: unalloca...@exim.org
Reporter: e...@ancel1.fr
CC: exim-dev@lists.exim.org
When a message is successfully delivered, Exim looks in the queue if other
messages can be delivered through the existing TCP/IP connection.
However, Exim only looks for the host address, not the host/port tuple.
When relaying multiple domains with manual routes to the same host address but
different TCP port, like so:
- a.domain.tld: 1.2.3.4::2525
- b.domain.tld: 1.2.3.4::2526
- c.domain.tld: 1.2.3.4::2527
Email from one domain might be delivered to the wrong host/port tuple.
Here is an (redacted) example of sending an email to cont...@b.domain.tld where
1.2.3.4::2526 is not listening or blocked:
2025-02-13 20:20:06 1tiekj-0000000Cd9d-2KfJ <= a...@example.com H=some.host.tld
[1.1.1.1] P=esmtps X=TLS1.3:TLS_AES_256_GCM_SHA384:256 S=4207 DKIM=example.tld
id=a-b-c-...@example.com
2025-02-13 20:22:16 1tiekj-0000000Cd9d-2KfJ H=1.2.3.4 [1.2.3.4]:2526: Remote
host closed connection in response to initial connection
2025-02-13 20:22:16 1tiekj-0000000Cd9d-2KfJ == cont...@b.domain.tld R=relay
T=remote_smtp defer (-18) H=1.2.3.4 [1.2.3.4]:2526 DT=2m9s: Remote host closed
connection in response to initial connection
...
2025-02-13 20:23:37 1tieo4-0000000CiBD-2myr => some.recipi...@a.domain.tld
R=relay T=remote_smtp H=1.2.3.4 [1.2.3.4]:2525
X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 C="250 2.6.0 <xxxxx>
[InternalId=178172423307302, Hostname=mta.a.domain.tld] 49931 bytes in 0.199,
244,401 KB/sec Queued mail for delivery" DT=0s
2025-02-13 20:23:37 1tieo4-0000000CiBD-2myr Completed
...
2025-02-13 20:23:37 1tiekj-0000000Cd9d-2KfJ => cont...@b.domain.tld R=relay
T=remote_smtp H=1.2.3.4 [1.2.3.4]:2526*
X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 C="250 2.6.0 <a-b-c-...@example.com>
[InternalId=178172423307303, Hostname=mta.a.domain.tld] 5613 bytes in 0.149,
36,657 KB/sec Queued mail for delivery" DT=0s
2025-02-13 20:23:37 1tiekj-0000000Cd9d-2KfJ Completed
The mail has been delivered to the wrong host/port tuple (1.2.3.4::2525 instead
of 1.2.3.4::2526), and the log says it has been delivered to the configured
host and not the one it has been actually delivered to.
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