If the AuthMechanism attribute on a Receive connector contains the value ExchangeServer, you must set the FQDN parameter ...

If the AuthMechanism attribute on a Receive connector contains the value ExchangeServer, you must set the FQDN parameter on the Receive connector to one of the following values: the FQDN of the transport server "{0}", the NetBIOS name of the transport server "{1}", or $null.