my $esc         = '\\\\';
my $period      = '\.';
my $space       = '\040';
my $open_br     = '\[';
my $close_br    = '\]';
my $nonASCII    = '\x80-\xff';
my $ctrl        = '\000-\037';
my $cr_list     = '\n\015';
my $qtext       = qq/[^$esc$nonASCII$cr_list\"]/; # "
my $dtext       = qq/[^$esc$nonASCII$cr_list$open_br$close_br]/;
my $quoted_pair = qq<$esc>.qq<[^$nonASCII]>;
my $atom_char   = qq/[^($space)<>\@,;:\".$esc$open_br$close_br$ctrl$no
+nASCII]/;
my $atom        = qq<$atom_char+(?!$atom_char)>;
my $quoted_str  = qq<\"$qtext*(?:$quoted_pair$qtext*)*\">;
my $word        = qq<(?:$atom|$quoted_str)>;
my $domain_ref  = $atom;
my $domain_lit  = qq<$open_br(?:$dtext|$quoted_pair)*$close_br>;
my $sub_domain  = qq<(?:$domain_ref|$domain_lit)>;
my $domain      = qq<$sub_domain(?:$period$sub_domain)*>;
my $local_part  = qq<$word(?:$word|$period)*>;

my $Addr_spec_re   = qr<$local_part\@$domain>;

#   Is an address valid?
if ( $address =~ /^$Addr_spec_re$/o ) {

    #   Yes
}
else {

    #   No
}
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