It depends how much money you can afford. One year you won’t get even with Microsoft or Google they have 30 days.
I do backups with snapshots on virtual disk level plus a regular backup with Veeam of my mailcow VM.
I have a Recovery Point Objective of 8 hours (2 snapshots at 12:00 and 20:00 and the regular backup at 04:00. and I keep those daily Veeam Backups (incremental forever) for about 45 days.
In case I need to restore something, I restore the VM aside the others, keep it offline, and restore the needed data with e.g. sogo-tools, and copy the data over to the running mailcow VM.