Private messages to admin only?

Hello,

I am trying to find a plugin or a method of allowing registered users to send private messages to the admin(s). I found plenty of private messaging plugins but they all seem to allow all users to have contact with each other – I only want users to have PM access to the admins.

Is there a way to do this? I did my best trying to search for an existing plugin but I may have missed something obvious (seems to always happen…)

Thanks in advance for your time and suggestions.