Transmittable and Nontransmittable Properties

MAPI defines some message properties as transmittable and nontransmittable. The information store performs local delivery of messages, which means that if a message's destination is within the same store, the information store—not the message transfer agent—delivers the message. In cases of local delivery, and to facilitate single-instance storage of messages, Microsoft Exchange Server generally transmits properties in the nontransmittable range when delivering messages to local destinations.