Every year end, I back up all of my client folders (monthly folders in each client's main folder) from the OST to a brand new PST labeled ClientName YYYY. I do it by opening the PST, right clicking the folder in the OST and selecting "Move"...

This worked great for all but one client today. For this client, only 10 folders copied from the OST to the PST (April and May are completely missing) and of the 10 that copied, 9 are empty (only August seems intact).

On my webmail server, all folders except April and May are still in the original location (as they were on the OST) but most are missing many emails.

Any idea how I can trouble shoot where all of these missing emails went and get them back? It's like a bunch just got "dropped" in transition.