i dont think there is a perfect system even with exchange if an email hits when there is a power outage or host failure it may still be lost even with a multiple DAG setup.
Having ZFS take a non intrusive storage snapshot at regular intervals will provide similar results then using "Shadow Copies" but they will be more resilient than SC as these can and do corrupt, we've even seen them completely disappear with a host crash.
Taking the ZFS snapshot will be more consistent than SC and more robust with the same outcome to be able to restore files from the Windows UI in the event that emails need to be recovered.
If SM used a Database instead of individual flies for emails then i would suspect that using VSS would be needed, but because the only DB entries are for indexing this can be rebuilt from the UI if there is an issue.
ZFS replication can be used to send to another ZFS system as a backup using the snapshots as the replication factor i.e. every 5 min, every 15 min, every hour etc.
In the event of ransom-ware then the roll back can be quick with ZFS much faster then restoring from a backup min vs hours.
any hoo we are still playing with the concept and will do some testing shortly, really just feeling out others experience and suggestions in this area.
thanks for the replies and input.