The following are the address properties for the current message sender:
PR_SENDER_ADDRTYPE
PR_SENDER_EMAIL_ADDRESS
PR_SENDER_ENTRYID
PR_SENDER_NAME
PR_SENDER_SEARCH_KEY
Transport providers are required to set the PR_SENDER_ properties to supply information about a message's originator. Transport providers set these properties on outgoing messages. When a message is sent to a variety of recipients with several messaging systems, each transmitted copy will have a different sender identity.
For more information on the address properties, see Base Address Properties.