Perl subroutine to validate e-mail addresses

    sub is_valid_email ($) {
       my ($addr) = @_;
       my $atext = qr/[A-Za-z0-9\!\#\$\%\&\'\*\+\-\/\=\?\^\_\`\{\|\+\~]/;
       my $dot_atom_text = qr/$atext+(\.$atext+)*/;

       my $no_ws_ctl_char = qr/[\x01-\x08\x0b\x0c\x0e-\x1f\x7f]/;
       my $qtext_char = qr/([\x21\x23-\x5b\x5d-\x7e]|$no_ws_ctl_char)/;
       my $text = qr/[\x01-\x09\x0b\x0c\x0e-\x7f]/;
       my $qtext = qr/($qtext_char|\\$text)*/;
       my $quoted_string = qr/"$qtext"/;

       my $quotedpair = qr/\\$text/;
       my $dtext = qr/[\x21-\x5a\x5e-\x7e\x01-\x08\x0b\x0c\x0e-\x1f\x7f]/;
       my $dcontent = qr/($dtext|$quotedpair)/;       
       my $domain_literal = qr/\[(${dcontent})*\]/;

       if ( $addr =~ /^($dot_atom_text|$quoted_string)\@($dot_atom_text|$domain_literal)$/ ) {
               return 1;
       } else {
               return 0;
       }
   }