Migration from Exim to Exchange 2013

Hi,

I have a Linux Mail server running Exim, with 1000 users.

The higher ups want the firm to migrate to Exchange 2013.

From what I've seen on the Exchange Server, there is no in-built migration tool, and online sources are rather scanty on any successful migration from Exim to Exchange. 

Any ideas on how to do this, without resorting to manually importing individual PSTs?

Thanks.