use Socket; 
use strict;
my $addy = shift || die "Enter a IP address";
my $port = getservbyname('smtp', 'tcp');
my $sin = sockaddr_in($port,inet_aton($addy));
my $client = gethostbyaddr($sin, AF_INET); # get name
if ($client)
{
print $client, "\n\a";
}
else
{
print "no\n";
}