There are probably better ways of doing this, but when pressed for an answer one day this is that I came up with. The idea was to parse a text field from a CGI form that supposedly contained a valid E-Mail address. Not only did we want to see if the address was formed correctly but the desire was to make sure that it was deliverable. If you have suggestions on how to improve on it I'd be very happy to hear from you. 
sub emailValid {
  my $email=shift;   # This is the addr to test
  my $t=$email;      # We're gonna chop up $t mercilessly
  local *PIPE;
  my $nslookup;

  # A very simple stupid way to find nslookup.  It's gotta be here
  # somewhere....
  if ( -x "/usr/sbin/nslookup" ) {
    $nslookup = "/usr/sbin/nslookup";
  } else {
    $nslookup = "/usr/bin/nslookup";
  }

  #
  # Tokenize the mail address into user@domain syntax
  $t=~m:^(.*)\@(.*)$:;
  my($user,$domain)=($1,$2);

  return 1 if (! $user ) or ( $user eq '' ); # No user!
  return 2 if (! $domain ) or ( $domain eq '' ); # No domain!

  my $IFS=$/;  # Save that please...
  $/='';       # We're gonna make one big input...
  open(PIPE,"$nslookup -type=any $domain 2>&1 |")
    or carp "Cannot run $nslookup ! " . $! ;
  my @check=<PIPE>; #slurp!
  close PIPE;       # gulp!
  $/=$IFS;          # put that back.

  return 3 if grep /Non-existent/,@check;

  return 0; # Checks out ok...

}

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In reply to valid email addresses by blue_cowdawg

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