donating members, club member, paid traders, etc don't have ANY time restrictions on their PMing. They can PM as much as they want, as frequently as they want.
regular members can PM too, just one PM (with I think up to 50 members cc'd) every fine mins.
now this usually isn't a problem if you're fairly involved with SAU, the problem arises only if you come on SAU purely to sell stuff. If you have less thant 10 posts you don't get to PM... and honestly if you can't be arsed making 10 meaningful posts on SAU then I don't see why we have to go out of our way to make sure your browsing experience is all rainbows and butterflies..
honestly we just don't have the time to verify people or rely on "are you human" tests, cos eventually they'll be circumvented. this is the best way of keeping it in check. The postcount of 500 was an idea I've been tossing up, because if we set it to a post count under a 100 you'll just get people spamming the forums to get their postcount up. You've gotta be real dedicated to make 500 posts, and kinda what we're looking for if youwanna enjoy an unrestricted PMing experience. Plus its not like we're stopping you from browsing the forum or anything, its just limiting the PMs.
These measures weren't implemented to make money or raise revenue. Its to encourage people to get more active in SAU, join the local club etc, while at the same time weeding out spammers.