By way of further updates to this -
The box that has the 2.02 firmware and out of service -
I installed only 1 Seagate 3tb drive, format as Standard, and can do operations on the Outlook file without getting corruption - appears to work OK in this configuration.
I then installed a second drive - 500gb, and formatted as 1 RAID-1 497gb volume leaving remaining space blank. (Now the box is 1 3tb drive & 1 500gb drive / 2.02 firmware / RAID-1).
Copied only the Outlook .pst file do the drive.
Opened the file, deleted some messages and the file is corrupted - cannot be accessed & cannot be repaired.
My suspicion at this point (requires even more testing) is the problem is related to RAID-1 and firmware 2.02, and suspect would have same problem with 2 drives of any size.... I will see if can find another spare drive to test this theory. Would seem to be consistent with other reports on this board of data corruption with 2.02 firmware.....
And, I am 100% convinced now that I should NEVER have bought D-LINK product - ONE MONTH after putting a support request in for this issue, I get a reply that says:
"These units are not meant to be used for database, they are more for your backup's. Microsoft doesn't recommend that have your PST files run from a network storage."
Wow, all I can say is wow. Even though the BOX for the DNS-320 calls this device "Network Storage" and the FIRST item on the box says "Share files over your network", and it has a box at the top with the text "Share Center-> Central storage + Gigabit connectivity for your network" - apparently it's not really meant to be used to share files over the network - it's just a backup device?

This is really unbelievable.