$html =~ s|(<[aA]\b                      # <a
            [^<>]*\b                     # any attributes
            [hH][rR][eE][fF]=\"?         # href=
              [mM][aA][iI][lL][tT][oO]:  # mailto:
              ([^\"\s<>]+)               # EMAIL
            \"?                          # href closed
            [^<>]*                       # any attributes
          >                              # anchor closed
            (.+?)                        # TEXT
          </[aA]>)                       # </a>

         |antispamize($1, $2, $3)|sgex;

sub antispamize {
    my($anchor, $email, $text) = @_;

    #$email =~ s/@/{at}/g;
    #$text =~ s/@/{at}/g;

    my $anchor = "<script language=\"JavaScript\">document.write('" .
            join("'+'", $anchor =~ /(.{1,4})/g) .
            "');</script>";

    ## may be you want to add this
    #$anchor .= "<noscript>$text ($email)</noscript>";

    return $anchor;
}