I can't find any real documentation on the quoted-printable-encode stream filter, but I've gathered info from several places. It seems there are 4 options that can be passed in the param array as in my other note on this subject:
line-length: integer, simply sets line length before a soft break is inserted
line-break-chars: Which char or chars to consider as a line break - note that "\r\n" will only match CRLF, not CR or LF, so make sure it matches your content.
binary: boolean, hex encodes all control chars, including spaces and line breaks, but leaves alphanumerics untouched
force-encode-first: Forcibly hex-encodes the first char on each line, even if it's alphanumeric. This is useful for avoiding corruption in some incompetent mail servers, like Exchange.
