Limitations / Considerations

Existing mailboxes will resolve to users with the same display name. As a result, you will no longer be able to edit it through in CP.
Passwords do not sync. A random password is generated upon mailbox creation.
Password changes do sync. Provided the password filter agent is installed properly. So after the mailbox is created, if the password is change in your AD, the new password will change in the CP.
Distribution list do not sync.
If the distribution list is manually created in the CP, members will sync from your AD. User's removed from the DL in your AD will not be removed from the DL in the CP.