I prefer OpenBSD and am much more familiar with it than Linux. I already have a VPS running OpenBSD and would rather not pay for a second VPS to run a mail server under Linux. On the other had I understand that setting up a complete, secure, email server from scratch can be a pain in the neck, have done it once before. Thus I am wondering if there is any email in a box for OpenBSD or how hard it would be to adapt the Linux system (collection of settings and mail software) to work on OpenBSD. Thank you.
Docker + Mailcow
or
MailInABox in an Ubuntu VM on your VPS (using qemu or similar)