The Forefront Identity Manager Service cannot connect to the Exchange Web Service because its credentials were rejected. ...

The Forefront Identity Manager Service cannot connect to the Exchange Web Service because its credentials were rejected.

The account under which the Forefront Identity Manager Service runs does not have permission access the service mailbox.  Alternatively, the configured mailbox may be incorrect.

Verify that the service mailbox has permission to connect to Exchange Web Services.  Also, verify that the mailbox is configured correctly in the application configuration file.