Hello
I managed to have a working postfix configuration (10/10 on mail-tester and spamhaus ok), especially because I have myhostname in main.cf set to the hostname of my VPS (set with hostname and hostnamectl commands).
At midnight last night I see main.cf was changed (automatically), and myhostname reset to the previous version 
What caused this, and how can I fix it?
thanks a lot for your help