Goals
* Restrict private messaging and emailing based on post count
* Simple installation via mybb plugin manager, with no core modifications
* Disabling of plugin via mybb settings to retain settings in database
* Allow admin to change the number of posts needed
* Allow admin to change the message displayed to members with under the required posts

Simple Installation
Upload contact_restriction.php to ./inc/plugins
Enable in mybb plugin manager
Go to mybb settings and setup

Quelle: http://mods.mybboard.net/archive/view/contact-restriction