NAME
    MIMEHeader - perform regexp tests against MIME headers

SYNOPSIS
      loadplugin    Mail::SpamAssassin::Plugin::MIMEHeader
      mimeheader    NAME_OF_RULE    Content-Id =~ /foo/

DESCRIPTION
    This plugin allows regexp rules to be written against MIME headers in
    the message.

RULE DEFINITIONS AND PRIVILEGED SETTINGS
    mimeheader NAME_OF_RULE Header-Name =~ /pattern/modifiers
        Specify a rule. "NAME_OF_RULE" is the name of the rule to be used,
        "Header-Name" is the name of the MIME header to check, and
        "/pattern/modifiers" is the Perl regular expression to match against
        this.

        Note that in a message of multiple parts, each header will be
        checked against the pattern separately. In other words, if multiple
        parts have a 'Content-Type' header, each header's value will be
        tested individually as a separate string.

        Header names are considered case-insensitive.

        The header values are normally cleaned up a little; for example,
        whitespace around the newline character in "folded" headers will be
        replaced with a single space. Append ":raw" to the header name to
        retrieve the raw, undecoded value, including pristine whitespace,
        instead.