Headers occur before the message body and are terminated by a null line (i.e., two contiguous CRLFs).
A line which continues a header field begins with a SPACE or HTAB character, while a line beginning a field starts with a printable character which is not a colon.
A field-name consists of one or more printable characters (excluding colon, space, and control-characters). A field-name MUST be contained on one line. Upper and lower case are not distinguished when comparing field-names.