YunoHost existing user authentication issue

I have searched the forum for similar issues

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This category is for general issues regarding YunoHost, NOT apps.

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This form is written in English :uk: but feel free to write in French :fr: if you’re more comfortable!

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What type of hardware are you using

Virtual machine

What YunoHost version are you running

11.2.30.2

How are you able to access your server

SSH

Are you in a special context or did you perform specific tweaking on your YunoHost instance ?

No

Describe your issue

Hello,
I have no idea what happened.
The only symptom at the moment, I have a number of existing users whose authentication fails both on the portal (Incorrect account name or password) and from an application such as FairEmail (The mail server said: [AUTHENTICATIONFAILED]).
Thank you in advance for your help.
Kind regards,
Steve

Share relevant logs or error messages

No message is available currently

That’s very suspicious. Do all the users have lost access to the server? Is there something in common between these users?
Check nginx error logs
Check fail2ban logs
Do you have uncommon apps or not updated apps?
If everything is OK, check the server with a malware scanner

Hello,

Not all users have lost access to the server. I have several users that continue to access to the different apps.

Users have something common: the account name of the working one start with letters between t-z. The one that has issue have account name starting with letters between a-s.

What should I look for in these log files?

No uncommon apps, and update are made every 2-3 weeks.

Which malware scanner ? rkhunter or chkrootkit ?

I found a clue, last time FailEmail was able to authenticate is 21:30 CET 13 october 2024…

I reset an account password this morning and this account is accessible again.

Which malware scanner do you recommend?
Are rkhunter and chkrootkit enough?

Important information I forgot to mention: the server only exposes ports 25, 587 and 993 on the WEB