Any time I upgrade my web server, mail is always the part I find a pita. Setting up the mailboxes etc. The syntax of the config changes all the time between distros, file locations are different etc so can't import the old config either. Tutorials also tend to be hit and miss as you really need to find one that is specific to your distro. Mail is usually what I spend the most time on in the setup process.

Is there some kind of script or tool I can use that automates this stuff better? Kind of like cpanel but without the price tag.

Till soem time ago I also configured my mailserver, postfix and dovecot. Normally during upgrade you'll be asked what to do with changes and/or differences in conf files.
Now I removed postfix and dovecot and started using Mailcow. Mailcow included postfix, dovecot, nginx, spamd, etc, in docker containers, and i very easy to upgrade by script. Maybe that is something for you too.

I'll have to play around with that and see. My original goal was always to just try to automate it myself but since the config file syntax/location/format etc changes so much between distros it makes it harder to automate.