mb_encode_mimeheader() encodes a given string
str by the MIME header encoding scheme.
Returns a converted version of the string represented in ASCII.
charset specifies the name of the character set
str is represented in. The default value
is determined by the current NLS setting (mbstring.language).
transfer_encoding specifies the scheme of MIME
encoding. It should be either "B" (Base64) or
"Q" (Quoted-Printable). Falls back to
"B" if not given.
linefeed specifies the EOL (end-of-line) marker
with which mb_encode_mimeheader() performs
line-folding (a RFC term,
the act of breaking a line longer than a certain length into multiple
lines. The length is currently hard-coded to 74 characters).
Falls back to "\r\n" (CRLF) if not given.
Note: This function isn't designed to break lines at higher-level contextual break points (word boundaries, etc.). This behaviour may clutter up the original string with unexpected spaces.
indent was added as of PHP 5.
See also mb_decode_mimeheader().