Old pm nag message

[RustedBucket]

Is there a mod or plugin out there that turns on some kind of nag message when a users stored pm's goes past a certain time? For the life of me, I can't understand why people feel it necessary to store pm's like emails and never clean themout. I'd like to be able to turn on a nag screen or better yet, just have a cron job that run nightly and deletes all pms past a certain age, say 180 days. It's not like they can't save these to their own pcs if they want to keep them.

Thanks