Hi, I'll usually delete the PM's in inbox of DP forum once it crossed 96% (960 messages). Initially I'll delete the sent messages and then I'll delete the received messages until my inbox shows 75% filled up position. How are you deleting the messages in your inbox?
When I hit around 90% but I still haven't experienced it yet and some of my messages are automatically deleted.
It depends if I have a job and all the details are in the job then I will delete them after the job is complete. Anything else gets deleted when i'm bored and need something to do, so maybe every other day.