I have 4 seed boxes I run on pia. My only issue is that the port changes from time to time. I have to check on them every week or so. It’s also one of the only court tested Vpns, though it did change hands after that
Edit: Turns out the pia client has a bash accessible command to get the active port. And Qbittorrent has a curl-able target to set the value. One bash script and a crontab… and now I don’t ever have to deal with the port changes anymore. You’re welcome leechers!
Use anything… Mailcow or otherwise. Just don’t expose the ports on your firewall/router to connect back to you.