#!/usr/bin/perl -w

use strict;
use Net::Ping;

my $host;
print "Host to ping? ";
chomp( $host = <STDIN> );
my $p = Net::Ping->new();
if( $p->ping($host) )
{
  print "$host is alive!\n";
}

else
{
  print "$host appears to be dead.\n";
}

$p->close();
[download]

You can do as follow:

use Net::SMTP;

@verify = ('smtp.host1.tld', 'smtp.host2.tld');

foreach $host (@verify)
{
        $smtp = Net::SMTP->new($host);
        if (ref($smtp))
        {
                print $smtp->banner();
        }
        else
        {
                print "failed $host!\n";
        }
}
[download]

This kind of check probably is better than pinging a host, but still doesn't tell you what is happening. A better solution would be to download a file from every remote host to be checked; if you can make these files contain some useful informations, like uptime, load average and disk usage, you can check what is happening and prevent also some kind of errors (i.e. disk full).
You can generate those files automatically via a cron job and download them via HTTP or FTP, as you prefer.

Ciao, Valerio