I prefer users take care of their own email and here's why.
Considering two hundred users emailing each other instead of talking, with emails averaging in size of 5+ megs, their inbox fill up within weeks. There's no way to avoid that. We have dumb users from top to bottom. The boss will yell at you like you don't know what you're doing when they hit the limit and start getting warning popups. Heck everyone's a boss here.
Yeah sure, when they crash sorry that's how it is. Start anew. No big deal, all junks anyway. They're glad they get rid all that junk anyway.
But if you leave everything on the server, and you do cleanup and deleted a "deleted" email from 4 years ago, you'll get yelled at for deleting that "deleted" email, because they needed it. (If it was a crash of their harddrive, they know the lost it, permanently, so they get around it or recreate their work. Now they have a reasonable excuse to their boss, because their harddrive crashed. Get the drift?..
Oh as for collaboration, they sure do collaborate by emailing left and right. They delete but never empty the trash, because "they might need it Someday"..
So to sum it up, they keep the email on their pc, if they crash, great excuse to "get a new computer". Great the computer guys got some work to do. Great they dont have a computer for a day because they got a crash. Basically whoever keeps the email is liable. I sure don't want that liability. They are provided network share drives to store whatever is "that important". (That I have to provide.)
Being negative or not, this is the way it goes if liabilty for cleaning up "deleted" emails is so high here. We only provide the service of flowing emails, not storing emails or safekeeping their junks.