Can someone share the proper way to upgrade Debian 11 > 12.
Are there specific config files that need to be replaced during the upgrade process?
That typically breaks things. If you are going to replace config files, you will need to compare them yourself and be certain that you do not introduce any breaking changes.
Always never replace the config files
And then only update exim config from /install/deb/exim/ file the last version
Then it should be fine …