Moving from Win to Linux

I have a client with an old mostly html site (there is on .asp page) on win6 and they want us to redevelop their site on WordPress. I would like to build out the new site on a Linux Server and then move their domain. The problem is that they store most of their mail on the servers.

I am wondering if there is a way to have a client moved to a linux server but keep their mail servers as they are.
Sorry, there is no automated move process in H-Sphere from Windows server to Linux server or vice versa.You have to manually move domain from Windows account to a Linux account and have to re-create all mailboxes after move.