I would have to say that your best bet (assuming I understand you correctly) is Mail::Box or Mail::Box::Manager. It's located here.

Assuming that you are using mbox format for your mailboxes:

 use Mail::Box::Manager;

 my $mgr    = Mail::Box::Manager->new;
 my $folder = $mgr->open(folder => $ARGV[0])
   or die("Mailbox open error: $!");
 print $folder->name. ": ".$folder->messages ." Total Messages\n";

 # Iterate over the messages
 foreach (@$folder) { print "Message $_"; }
 $mgr->close()
  or die("Mailbox close error: $!");
[download]

Untested.