A one-off address template should contain a check box with which the user can set the MAPI-Recipient property for one-off addresses. When a user creates a one-off address for backboning a message to a MAPI-based recipient, the user can set the MAPI-Recipient property to TRUE. (The default value for this property is FALSE.) If the property is set on a one-off address, it is maintained in the personal address book (PAB) and will be automatically set in the future when the user addresses a message using the PAB.
The gateway should check incoming messages with one-off addresses to see if they contain TNEF attachments. If a one-off message contains TNEF, it is a backboned message and its MAPI-Recipient property should be set to TRUE. The gateway should also set the MAPI-Recipient property on the originator of the message so replies can be encapsulated for return.