2.2.3.2.3 References

To set the value of the PidTagInternetReferences property ([MS-OXCMSG] section 2.2.1.26), clients write the value to a References header.

MIME readers copy the value of the References header to the value of the PidTagInternetReferences property. MIME readers MAY truncate the value of the PidTagInternetReferences property if it exceeds 64 kilobytes in length.