2.2.3.4.1.2 Content Type
MIME readers SHOULD save the value of the Content-Type header in the PidTagAttachMimeTag property ([MS-OXCMSG] section 2.2.2.29) during MIME analysis. The following notes apply for specific values of this header:
The "application/ms-tnef" value SHOULD<159> be replaced with "application/octet-stream". This is in the rare case when a TNEF body part is corrupt and cannot be completely processed. Ordinarily, a TNEF body part SHOULD NOT be written to an attachment, but analyzed into Message object properties and discarded.
The values "application/x-pkcs7-MIME" and "application/pkcs7-MIME": the entire Content-Type header value, including all parameter names and values, SHOULD be written to the PidNameContentType property ([MS-OXPROPS] section 2.414).
For Content-Type header values that start with "text/", if a charset parameter is present, the parameter value SHOULD be written to the PidTagTextAttachmentCharset property ([MS-OXCMSG] section 2.2.2.25).