2.2.2.1.2.1 Incoming Text Message

To compose the message body for an incoming text message, the server MUST create a plain text MIME part for the text message content by adding the following headers:

Content-Type: text/plain; charset=xxxx

Content-Transfer-Encoding: quoted-printable

Examples of valid charset values are "us-ascii" (ASCII) and "gb2312" (Simplified Chinese). The server can also use multipart/alternative content type and provide a HTML view of the message body. A reference of valid charset values can be found in [IANA-CharSets].