Customized entries in
get reverted after the command
was run, Plesk microupdates were installed, or after changing settings in Tools & Settings > Mail Server Settings. Why does it get reverted?
plesk repair mail
Intended behavior. Plesk re-writes the config file every time mail settings are changed.
A vote can be left on Plesk UserVoice regarding the feature of keeping customizations untouched by Plesk:
Allow customization of /etc/postfix/main.cf.
The top-ranked suggestions are likely to be included in the next versions of Plesk.