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SOLVED: Suddenly, one of my servers running SmarterMail 9364 on Debian 12 stopped receiving external emails, and the SMTP log is filled with this:

Problem reported by Gabriele Maoret - SERSIS - 8/26/2025 at 6:28 AM

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HELP! Suddenly, one of my servers running SmarterMail 9364 on Debian 12 stopped receiving external emails, and the SMTP log is filled with this:

[2025.08.26] 15:13:58.063 [251.380.362.290][43106295] "421 Server is busy, try again later." response returned.

[2025.08.26] 15:13:58.063 [251.380.362.290][43106295] IP 251.380.362.290 rejected for proxy. Reason: not a configured proxy.

[2025.08.26] 15:13:58.063 [251.380.362.290][43106295] disconnected at 26/08/2025 15:13:58

Please note that the IP 251.380.362.290 is a fake IP for privacy reasons...

What could be the reason? (Nothing has changed in the configuration...)

I've already tried restarting the server, but nothing has changed.

Everything was working fine until 1:32 PM (Italy), then it started doing this...

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)

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Gabriele Maoret - SERSIS Replied

8/26/2025 at 6:46 AM

Solved... My fault...

I added a WHITELISTI IP and enabled this option (TCP Proxy):

That messed everything up.

I disabled it and now it's working again:

I don't know what is it for, but be aware!!!!!

Can this be a BUG?

It blocket EVERY incoming email from everywhere....

I'll open a new post for asking that...

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

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