How to Trust the Default SSL Certificate in Exchange 2007
http://technet.microsoft.com/en-us/library/bb400931%28EXCHG.80%29.aspx
To perform the following procedure, the account you use must be delegated the Exchange View-Only Administrator role.
For more information about permissions, delegating roles, and the rights that are required to administer Exchange Server 2007, see Permission Considerations.
Procedure
To use the Exchange Management Shell to determine the thumbprint of the existing self-signed certificate