So, if it was like the scenario at my workplace, at that same time period we were stuck with an obscenely low (50MB) MS Exchange inbox limit (since bumped to a "whopping" 100MB), which forces you to sort everything to local PST files (which default to encrypted-format), then had lowest-bidder full disk encryption on top of that (quite possibly GuardianEdge). The version of GuardianEdge in use at the time had a nasty tendency to crash harddrives... of my office of 28 persons, all 28 had an unrecoverable harddrive crash during that same time period. To compound things, GuardianEdge would also encrypt external USB drives, but the encryption key was stored on the internal drive. Personnal network partitions were also too small at the time to back anything up to the network.
But, in spite of all this, it's still way too "convenient" that these emails were lost.