Exchange with Postfix

Hi!
I have a question regarding implementation of Exchange server. We have a mail server on Linux in our company. due to variety of functions we’d like to implement an Exchange server for our employees. However since our customers already have some mailboxes on linux we’d like to keep existing mail server and add Exchange. The point of it would be to download mail from linux server for specific mailboxes and distibute it to AD mailboxes. Can it be done?

Cheers,
Vlado