The following are the address properties for a messaging user being represented by the original sender:
PR_ORIGINAL_SENT_REPRESENTING_ADDRTYPE
PR_ORIGINAL_SENT_REPRESENTING_EMAIL_ADDRESS
PR_ORIGINAL_SENT_REPRESENTING_ENTRYID
PR_ORIGINAL_SENT_REPRESENTING_NAME
PR_ORIGINAL_SENT_REPRESENTING_SEARCH_KEY
For more information on the address properties, see Base Address Properties.