The following are the attachment properties for a message:
PR_ATTACH_ADDITIONAL_INFO
PR_ATTACH_CONTENT_BASE
PR_ATTACH_CONTENT_ID
PR_ATTACH_CONTENT_LOCATION
PR_ATTACH_DATA_BIN
PR_ATTACH_DATA_OBJ
PR_ATTACH_ENCODING
PR_ATTACH_EXTENSION
PR_ATTACH_FILENAME
PR_ATTACH_FLAGS
PR_ATTACH_LONG_FILENAME
PR_ATTACH_LONG_PATHNAME
PR_ATTACH_METHOD
PR_ATTACH_MIME_SEQUENCE
PR_ATTACH_MIME_TAG
PR_ATTACH_NUM
PR_ATTACH_PATHNAME
PR_ATTACH_RENDERING
PR_ATTACH_SIZE
PR_ATTACH_TAG
PR_ATTACH_TRANSPORT_NAME
PR_HASATTACH
PR_PHYSICAL_RENDITION_ATTRIBUTES
PR_RENDERING_POSITION
PR_TNEF_CORRELATION_KEY
For more information on attachments, see Attachments.