Unhelpful Exception with resetPrincipalCredential() when SMTP Server rejects email address

When using resetPrincipalCredential(), if the Exchange SMTP server rejects the email address, then all we get from resetPrincipalCredential() is the exception:

org.codehaus.xfire.XFireRuntimeException: Could not invoke service.. Nested exception is org.codehaus.xfire.fault.XFireFault: Invalid Addresses

Our company's Exchange server is configured to reject any SMTP emails addressed outside the company. Addresses inside work okay, but with the above exception we can't easily catch those to format a user-friendly error message.