O Suporte da Apple tem um tópico que explica como fazer isso em detalhes.
1. Open Mail (click its icon in the Dock, or open it in the Applications folder).
2. From the Mail menu, choose Preferences.
3. Click Accounts in the toolbar.
4. Click the + icon. The "Add Account" sheet appears.
Enter your real name, email address, and password;
click Continue. If Autodiscovery is enabled you can
skip to step 8.
Note: If you do not know what to enter for any of these,
contact your Exchange administrator.
Note: If the Exchange server does not have Autodiscovery
enabled, you will need to manually fill in your mail server
information fields mentioned below (go to step 6).
5. The "Incoming Mail Server" sheet appears.
6. Select Exchange 2007 from the Account Type pop-up menu
(the type of Exchange server you want to use is a
Client Access Server (CAS) ), enter an optional description,
enter the incoming mail server address, your user name, and
password.
If you do not know what to enter for any of these, contact your
Exchange administrator.
7. Select "Address Book contacts" and/or "iCal calendars" if you would
like to automatically configure iCal and Address Book for use with
your Exchange server as well.
8. Click Continue. The "Account Summary" sheet appears.
9. Review the information in the summary. If it appears to be correct,
click Create. If you need to make changes, click Go Back.
Note: Select "Take account online" to take this account online immediately.