You can do this by going to: ACP (Admin Panel) > General > Messages and e-mails > Private messages > Private Messaging > Minimum posts before sending private messages : , set the number to what you want and hit save.
Hope this helps,
-Brandon
P.s I see you set your language to greek, just do you know there is a greek support forum as well, just wanted to let you know in case you didn't know .
Thanks for your answer! I want to set a limit of 500 posts for allow a member to send a private message. Can this be done? Thanks too for your information about the Greek support forum. I will keep this in mind
It is highly possible then that the limitation for this feature is that you can not set it for anymore then 200 posts. If this is the case, there is nothing you or we can do to change this .