Not OP, but I run both because Plex was/is easier to setup non-techy family members and easier to get on their TVs/devices.
Plex has been pissing me off though and I’d like to move to Jellyfin, but sounds like a PITA to transfer everything over. Gonna have to get clever with that probably
Purely Mail, yes; so long as you’re comfortable with one guy running the service.
Thunderbird for desktop and K-9 for Andriod. Only because they were the most recommended and completely fit my needs.