How do I activate PMs?

I have "No PMs" next to my name on posts, and I can't find the option to activate PMs (it's not that I want to start harrassing anyone... yet!).

Is there a way to activate them, or does it come automatically?

Thanks, Al

It's an automatic thing after x number of posts. Obviously x is higher than 21 :D

I'm pretty sure it's 25 posts.

It was supposed to be set down to 12 but this obviously never happened.

I seem to remember it being 30 ... but it's been a while so I might be mis-remembering. as usual.