Apple Mail Sync Issues with Exchange

Hi,

We are having some issues with adding a Microsoft Exchange account to Apple Mail. The account just seems to freeze once added, it does not appear to download any of the emails for the account, even when left over night. Not incoming emails appear in the inbox at all, the user is able to send emails out from the application, but it stays in the outbox for 5-10 minutes. The only time we are able to to "sync" emails is when the account is added or the mailbox rebuilt, but this only last for a few minutes before nothing at all seems to happen. I left the Mac to download emails last night, it was at 4,729 and in the morning it was at 4,752.

Can anyone advise on this?

Many Thanks,