Convenient "PM" for the forum, free and not, asp.net mvc3?

Question

ASP.NET

Hello.
On my site, visitors use private messages very heavily, some receive and send more than 50 messages a day. The "classic" construction of "lichka" is inconvenient and difficult. Please advise a private messaging system for forums that would meet the following requirements:
- Written in ASP.Net MVC 3
- Easily integrated into existing sites
- Organizing messages into conversations
- Full-text message search
- Availability of an address book (site users can optionally be added to address book)
- Combining users into groups (any user makes a group for himself)
- Organizing messages into folders of the user's choice.
- Acceptable display on mobile devices.
Thanks for the advice.

Answer 1

I would remove the mvc3 requirement and answers might appear for everything else.
Or are you going to finish it yourself?