use Net::DNS::Resolver;

my $domain = 'example.com';
my $dns    = Net::DNS::Resolver->new;
my $valid  = $dns->query($domain, 'MX')
             || gethostbyname($domain);
printf(
   "You could %s send mail to %s.\n",
   ($valid ? "maybe" : "not"),
   $domain,
   );