MAPI properties runs from 0001 to 3FFF
4000 to 7FFF belongs to message and recipient properties, and either clients or service providers can define properties in this range
Named properties – 8000 onwards
Secure profile properties for Service providers – 0x67F0 through 0x67FF
When we use Named properties, MAPI picks up an available property identifier. This way it avoids conflict with the properties that are being used by MAPI clients like Outlook.
Non-transmittable properties usually contain information that is of value only to clients and service providers operating with the current session. These properties would not necessarily be useful to another messaging system and another set of service providers.
A non-transmittable message property exposed at both the sending and receiving ends of a transmission, with different values depending upon the client application or store provider involved. This property is initialized by the client or message store provider when a message is created and saved for the first time and then updated periodically by the message store provider, a transport provider, and the MAPI spooler as the message is processed and its state changes.
Transmittable properties are transferred with a message; non-transmittable properties are not transferred with a message. The concept of transmittable properties applies primarily to transport providers.