2.2.3.8 attAttachData Attribute Handling by the TNEF Writer

The TNEF Writer can use the attAttachData attribute, as specified in section 2.1.3.3.11, for the attachment data if the PidTagAttachMethod property ([MS-OXCMSG] section 2.2.2.9) of the original attachment contains the value 0x0001 (ATTACH_BY_VALUE). If the PidTagAttachMethod of the original attachment contains the value 0x0005 (ATTACH_EMBEDDED_MSG) or the value 0x0006 (ATTACH_OLE), then the TNEF Writer MUST encode the data in attAttachment (section 2.1.3.4).