DO NOT host your own email server though. A couple of decades ago it made perfect sense to do so, but these days it's simply not worth the trouble. Instead use Google/Outlook/Apple/Whatever to host your custom domain and use their offerings with your custom domain.
My personal domain is hosted by mxroute.com, which has served me well for a lot of years by now. Unlimited email accounts and the only restriction is storage, which i can upgrade. Very little downtime (none i've noticed).
All that's left is to make a backup with regular intervals, which i to do a small local machine using imapsync, which then in turn makes backups of the emails (and regular data) to a local drive and a cloud backup.