The "delete older than" trick was used at one of my old companies. We were constantly getting calls to "restore that vital email!". What is in use at my current job is a max mailbox size. They hit the wall, no more send/receive till they free up space. If it is space concerns that are triggering this request, you may want to consider some healthy, yet finite size limitation. We give them 35 Meg. Special cases get upped to a 100 Meg on manager's request.