Replication and backups are usually different things. If you need replication, yes, backup tools won't cut it latency wise. But proper backup tools like rsnaps

Replication and backups are usually different things. If you need replication, yes, backup tools won't cut it latency wise. But proper backup tools like rsnapshot, borg, etc. pp. have no trouble correctly backing up email servers even at 10 or 100 times your mail store size.