If you are looking to migrate from Lotus Domino or from a generic POP/IMAP mail server to Exchange 2007, I have good news! The (free) Microsoft Transport Suite has been updated, to allow for multithreaded import of POP/IMAP mailboxes, and now supports migration from Lotus Notes R8.x.
Where do I get it ? http://www.microsoft.com/technet/move
Or direct links:
Transporter Suite Release Notes Guidance
The February 2009 release includes the following major updates to the Transporter Suite for Internet Mail:
The February 2009 release includes the following major updates to the Transporter Suite for Lotus Domino: