2.2.3.2.25 Content-Base

To set the value of the PidNameContentBase property ([MS-OXCMSG] section 2.2.1.41), clients MUST write the value to a Content-Base header on a MIME entity that maps to a message body (top-level or nested), as specified in section 2.2.3.3, or on a Message object that corresponds to an attachment.

MIME readers SHOULD<136> copy the value of a Content-Base header on a top-level message to the value of the PidNameContentBase property.