Today I was working on a few user accounts who were way over the mailbox size I recommend (and soon will be putting a hard clamp down on). Here's the short story:

I logged in via RDP and ran TreeSize on the D: drive to see which domain/users folders were the largest. One customer showed up as having 712 GB of files on the HD. Drilling down I saw the "Deleted Items" folder contained 400 GRP files, all named 2023_12_5* through 2023_12_15*. I flipped over to the webmail interface, impersonated the user, and saw their "Deleted Items" folder was empty. These were, apparently, forgotten files by SmarterMail.

So, I took a chance. I flipped back over to the RDP window and selected all the GRP files and clicked Delete. Five minutes later I had reclaimed 700 GB of hard drive space. The user is back down to 12 GB, which is what the web interface is reporting.