Previous to Traveler 188.8.131.52 Traveler would not encrypt mail when the SentTo name picked on an iOS device was an internet e-mail address (e.g. firstname.lastname@example.org).
In 184.108.40.206, IBM changed the behavior so that the router would change the e-mail address into a Notes Name. However, the name does NOT resolve back to an Internet Address if the mail system is Other Internet Mail (5) and is forwarded off. Depending on if there is a Domain document and a connection, the router instead says that it cannot find a route to the domain (if not one) or that the user is not in the Address Book (if there is one).
via Traveler 220.127.116.11 Secondary Directory No Route / Not in Address Book Issue – Mindwatering Incorporated.