I am requesting any professional service for installation of IRM pro and server and Rainloop webmail then migrate existing account, mail content, contacts from atmail to IRM plus auto create sub-account on mailchimp at each time a new user registers.  You will have to modify the registration screen such that new users are only able to register with facebook connect.

This migration will be done on same server atmail is installed. Operating system is CentOS linus 6.7

If you are a professional and confident enough to do this please revert with an email address to contact you for further discussion.