After a while i was not able to send emails again.
I used the add or remove components tool in plesk to remove postfix and installed qmail.
Then i did it the other way around. I guess like @fhe did it.
After this i was able to send emails again.
Heres's what i found out:
1. No Change here...
I'm facing the same issue after updating to 18.0.34
But i can receive E-Mails. Just sending E-Mails is impossible.
stat /var/spool/postfix/plesk/passwd.db output:
File: /var/spool/postfix/plesk/passwd.db
Size: 36864 Blocks: 72 IO Block: 4096 regular file
Device...