I had that too - some insane bullshit of using it as a transfer point to sort stuff.
If I remember correctly (it's been a long time) the user I was dealing with was deleting messages he had dealt with, but got into the habit of referring back to the messages when necessary in the Trash folder. I suggested moving these sort of messages to another locally-stored folder, but the user refused saying "I'm used to working out of my Trash now."
I'd set up mail clients to empty Trash on exit, and when the guy that was doing this logged back in it was of course empty, so he came to rant at me in the lunch room to the amusement of all onlookers.
Logical. I considered trying that, but never did.
Now every few months he rings me up about a full disk, and each time I have to suggest emptying the Trash mail folder and the "Recycle Bin" on his desktop.
That reminds me... another thing that was going on back then was that a small set of users refused to delete any messages off the server, and at the time the server used MBOX storage and ext3 had a 2 GB filesize limit. One particular Sales guy got so much email that he would hit the 2 GB storage limit about every 3 months. He'd then call me up and tell me he wasn't getting his mail, I'd find his mailbox full, and I had to use 'mutt' to go delete old messages. I kept requesting to set his mail client to delete messages older than 3 months, but he kept refusing to allow me to do that. Instead he kept calling me every three months to fix his mailbox.
The next attempt at a fix was to make a script to watch mailbox sizes and warn the users of those mailboxes that were getting full to do something about it or to call me. I didn't expect that to work -- and it didn't -- but it was the next thing to try.
The final solution was to modify the "watch mailbox sizes" script to first warn the user about their mailbox size at a "soft" threshold, and let them know that when the mailbox size reaches a "hard" threshold that the system will automatically delete old messages out of their mailbox. I wrote another script that did just that, which (if I remember correctly) deleted messages that were older than 3 months. And with that, I never got another call about users reaching their mailbox size limits.
It's not that the person in question is stupid, it's that such people don't understand the design purpose of such items and use them in ways opposed to what was intended, which can sometimes produce useful results as well as just utter facepalms.
Right. Or they build up bad habits of using the system in a way that it wasn't designed for -- just like your story about the garbage bins used to store backup tapes. (Good story, BTW -- thanks.)