Content-transfer-encoding header field

This header field defines the content encoding of the message.

Valid values include:

• 7bit
• 8bit
• binary
• quoted-printable
• base64
• x-* - where * represents any token

If not specified, the Content-Transfer-Encoding defaults to 7bit.

7bit, 8bit and binary indicate that NO encoding has been applied. "x-token" permits additional encoding schemes, but its use is discouraged by the standard (RFC 2045).

If this field is used in the message header, it applies to the entire body of the message. If it appears in an entity header, then it applies only to that entity. If an entity is of type multipart then the encoding can only have values of 7bit, 8bit or binary.