Issue Postfix / Dovecot Problem / ePlesk 18.0.40 and Ubuntu 20 LTS

[Kulturmensch]

Suddenly I receive the following error messages for all incoming E-Mails:
Out: 220 mail.tenckhoff.de ESMTP Postfix (Ubuntu)
In: EHLO keeper-us-east-1b.mxtoolbox.com
Out: 250-mail.tenckhoff.de
Out: 250-PIPELINING
Out: 250-SIZE 51200000
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-AUTH DIGEST-MD5 CRAM-MD5 PLAIN LOGIN
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250-DSN
Out: 250 CHUNKING
In: MAIL FROM:<[email protected]>
Out: 250 2.1.0 Ok
In: RCPT TO:<[email protected]>
Out: 451 4.3.5 Server configuration error
In: QUIT
Out: 221 2.0.0 Bye

Trying to find out the error: Out: 451 4.3.5 Server configuration error
i tried first the webinterface troubleshooter and then plesk repair mail via ssh - both said: no errors.
Any idea how to find the problem?

 

[Kulturmensch]

The last error: 554 5.5.1 Error: no valid recipients

 

[Bitpalast]

To tackle this issue you need to look into /var/log/mail.log and check the entries that relate to exactly the one mail you are trying to send. You'll normally see more details there (beyond "configuration error").

Further, one reason for a general "configuration error" can be that the receiving server denies receiving mails from your system. This is sometimes not told (e.g. GMX, web.de do that, they don't say "we are not accepting mail from you", but sometimes behave as if there was no mail service at the recipient server).