use Net::DNS;
my $resolver = Net::DNS::Resolver->new;
my $domain = "perlmonks.org";
my $query = $resolver->query($domain,"MX");
if ($query) {
    # They have an MX record, send the mail.
} elsif (gethostbyname($domain)) {
    # No MX record, but the host exists.  Send the
    # mail.
} else {
    # No host, and no MX.  No mail for you!
}
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Cheers,
Paul

You can also do it like this to be a trifle more complete:

use Net::DNS; 
$res = new Net::DNS::Resolver;
warn "Net::DNS error $@\n" if $@;
# on some systems without the required config files you will need to
# direct Net::DNS to your DNS nameserver(s) or it will timeout
$res->nameservers( $prinary_nameserver_ip_address, $secondary... ) if 
+$res;

sub dns_query {
  return undef unless $res;
    my $domain = shift;
    $packet = $res->send($domain, 'MX') or warn $res->errorstring;
  return 1 if $packet->header->ancount;
    my $packet = $res->send($domain, 'A') or warn $res->errorstring;
  return 1 if $packet->header->ancount;
  return 0;             
}

print "OK DNS $domain" if dns_query($domain);
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Kanji notes my slack duplication of identical code. It is more maintainable to do this:

sub dns_query {
  return undef unless $res;
    my $domain = shift;
    for my $dns ( 'MX', 'A' ) {
        $packet = $res->send($domain, $dns ) or warn $res->errorstring
+;
      return 1 if $packet->header->ancount;
    }
  return 0;             
}
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

Mail can reach the baz.com domain if there is a Domain Name Service MX record defined for that domain. The MX record can point to any host. The host handling mail for baz.com doesn't have to be in the bax.com domain. It could be in the not-baz.net domain)

You can verify this with the nslookup command.

1. Type  nslookup at your UNIX / win2K or (?) NT command prompt
2. At the new prompt enter  set type=ANY
3. type  baz.com

email: mandog

• A (address) records map a domain name to an IP address, e.g. the A record for jonallen.info is 212.69.202.117.
• CNAME records are aliases - mail.jonallen.org.uk is an alias for www.jonallen.org.uk (they are physically the same machine).
• MX (mail exchange) records indicate the host which handles email for that domain - this does not have to be related to any other servers (e.g. web). Normal convention is to use email in the form user@domain.tld wheras webservers are usually called www.domain.tld. It is possible to have MX records for domains without A or CNAME records (either of which is required for a name to resolve to an IP address), this is causing your problem with gethostbyname().
  Several MX records can be set for a domain name, each with a priority value. For example, if I have an MX 5 record and an MX 10 record, email will be sent through the MX 10 host if the MX 5 machine goes down.

Have a look at http://www.dns.net/dnsrd/ for more information (try the 'DNS resource record types' link).

Cheers,

JJ

The Examples section of POD documentation for this module even includes some notes on DNS checks on email addresses.

From this POD ...

Examples

Let's see if the address 'maurice@hevanet.com' conforms to the RFC822 specification:

print (Email::Valid->address('maurice@hevanet.com') ? 'yes' : 'no');
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Additionally, let's make sure there's a mail host for it:

print (Email::Valid->address( -address => 'maurice@hevanet.com',
                              -mxcheck => 1 ) ? 'yes' : 'no');
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Let's see an example of how the address may be modified:

$addr = Email::Valid->address('Alfred Neuman <Neuman @ foo.bar>');
print "$addr\n"; # prints Neuman@foo.bar
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Need to determine why an address failed?

unless(Email::Valid->address('maurice@hevanet')) {
  print "address failed $Email::Valid::Details check.\n";
}
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If an error is encountered, an exception is raised. This is really only possible when performing DNS queries. Trap any exceptions by wrapping the call in an eval block:

eval {
  $addr = Email::Valid->address( -address => 'maurice@hevanet.com',
                                 -mxcheck => 1 );
};
warn "an error was encountered: $@" if $@;
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Ooohhh, Rob no beer function well without!

I'm no DNS expert, but in your example, baz.com probably has no record pointing to a server for 'baz.com'. There is an MX record that indicates the IP address of the default mail exchanger server, and that's probably what you'll have to query for if you want accurate results.

Using nslookup, you can query the MX record for baz.com with the following command:

nslookup -type=MX baz.com
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This should return something like the following:

baz.com preference = 10, mail exchanger = mail.baz.com
...
mail.baz.com    internet address = xxx.xxx.xxx.xxx
[download]

conv