how many of them can there be saved in the PM folder (inbox+sent)?
is there a difference between inbox and sent PM`s sizes?
...nihil nisi bonum
You can have a total of 50, counting messages received, sent, and being tracked. If you run out of room, try deleting them from the sent and tracking folders.
Actually, my messege box is usually considered full once it reaches 11 total messeges. I think if you are a moderator, that number is boosted to what Benito just said. Unless that's been changed recently?
It might depend on the size of the message. I've had dozens of them in my various folders at one time.
The limit is supposed to be 50, so if you've got fewer in your inbox, be sure to check that you don't have any more lying around in your sent box, etc. If you use message tracking, those will count against your saved items, too.