Hello!Connection hangs after DATA stage

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1

Hello!

I’m running KumoMTA on an Ubuntu 20.04 server. The configuration is almost identical to another server where everything works fine. However, on this server, when sending emails (especially test emails from MailWizz), the connection hangs at the DATA stage. Sometimes KumoMTA replies with 354, but then it times out. Logs show that processing reaches smtp_server_message_data but doesn’t continue.

Examples:

When connecting via telnet to an external SMTP (e.g., spamtest.smtp.bz), the connection opens but then stalls.
Using openssl s_client -starttls smtp, the TLS handshake completes successfully, certificate is valid.
I tried disabling auth and TLS — same result.
ulimit increased (ulimit -n 65535, ulimit -u 16384).
KumoMTA version: 2024.09.02.062344.c5476b89

Question: what can cause a timeout or hang after the DATA stage during outbound delivery, and how can I debug this behavior?

3

Can you print the debug log?

./kcli trace-smtp-server
4

I’m guessing a “data-dot” issue, but it is impossible to tell without more data ( see what I did there?)…
Like Blue Griffin asked, a trace would be helpful, but so would your full configs as requested in the note above.
Also, a tail of the journal would not hurt. You might have some logic that is failing at that stage and you wont see those errors outside the journal logs.

5

This was last updated 25 days ago so I am closing it. Go ahead and reopen if you still need answers.