As reported by some users GpgOl is unable to read the addresses of users if they
come from Exchange.

A bit research showed that there is a special ExchangeUserObject (
http://msdn.microsoft.com/en-us/library/cc513843%28v=office.12%29.aspx#AddressBooksAndRecipients_TheExchangeUserObject
) which is returned in case a recipient is in Exchange. This Object is currently
not handled by GpgOL