Hello all. I have been around a while and have accumulated some good information from members in my PM box. It's handy to reference a lot of these so I really don't want to delete them. If find my box at like 90% all the time and it gets to 100% pretty quick!
Become a moderator/administrator. That's about it, honestly. Increasing the PM mailbox size and having them get full for a lot of people who never empty them would drastically increase the database size and for doing weekly backups, or even more frequently would also take up a lot of storage. A site like SN probably has a several GB database.