Bill has a Windows desktop and a MacBook Pro and he wants to sync them together with email. He uses POP3. Leo says to stop using that, and use IMAP instead. IMAP is the best way to go because it doesn't take his email off the server. POP3 downloads email and then deletes it from the server. So Bill should go with IMAP and then he can have a central location for all of his email that's accessible from any device.
Can he transfer his old Outlook files to his new email? Leo says no. Outlook stores them into one giant file. So the best thing to do is archive the files into an 'archive.pst' file and then upload them to another machine. But he won't be able to transfer them to his new email server. They won't want to store them. Chances are that they will already be there if he moves over to IMAP.
The chatroom says that Gmail can import PST files. Then he'd have all that email. Outlook for Mac will do it as well.