2.1.3.3.3 Simple Plain Text Message Body

When the best body format type is plain text, MIME writers SHOULD generate a single MIME entity with the value of its Content-Type header set to "text/plain".

The charset parameter value of this MIME entity's Content-Type header SHOULD be set to a character set that corresponds to the value of the PidTagInternetCodepage property ([MS-OXCMSG] section 2.2.1.56.6), which is a code page number. If there is no PidTagInternetCodepage property, the value of the PidTagMessageCodepage property ([MS-OXCMSG] section 2.2.1.56.6) can be used instead, but in that case the message code page SHOULD first be mapped to the corresponding Internet code page. MIME writers SHOULD verify that the plain text, which is stored in UTF-16 form, can actually be encoded in this character set and SHOULD, if necessary, choose a different character set that can in fact encode the entire message body; the code page properties express a preference rather than a requirement.

The value of the PidTagBody property ([MS-OXCMSG] section 2.2.1.56.1) is written to the content of the "text/plain" MIME element, after being converted to the chosen character set.