mb_encode_mimeheader() converts string str to encoded-word for header field. It returns converted string in ASCII encoding.
charset is character encoding name. Default is ISO-2022-JP.
transfer-encoding is transfer encoding. It should be one of "B" (Base64) or "Q" (Quoted-Printable). Default is "B".
linefeed is end of line marker. Default is "\r\n" (CRLF).
Example 1. mb_convert_kana() example
See also mb_decode_mimeheader().