A transient failure has occurred. The problem may resolve itself in a while. The service will retry in 56 seconds. Diagnostic information: Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=PINNERGYLTD/cn=Microsoft System Attendant. Microsoft.Exchange.Data.Storage.ConnectionFailedTransientException: Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=PINNERGYLTD/cn=Microsoft System Attendant. ---> Microsoft.Mapi.MapiExceptionNetworkError: Why is this happening?

Your problem seems to be Exchange Server specific.For fast and accurate answers on Microsoft Exchange please post your question in one of the Microsoft Exchange Server Forums.Not all of us here (in the Server forums) have Exchange Server running or can reproduce your problem.