We are running Suse Linux 10.1 with Qmail, which we have set up as
a backup mail server (when our primary Windows server goes down we sometimes lose emails). The new mail server is located in the same offices as our domain, but is accessible via a direct non-domain IP for which we have no domain name. The upstream controller of our MX record can set that IP to be used if the Windows server is not responding.

DNS is running on the Suse box, but as a "caching" server (no zones defined). We expect to need the Suse box when the Windows server is down-- and the Windows server is the only "forwarder" we listed when we set up Suse DNS server. (The "forwarder" is actually in the Windows domain, and our Suse box also has a local LAN IP.)

The question is-- when the "forwarder" is down, will the SMTP server (in this case Qmail Toaster with SquirrelMail) be able to send emails to the net, or will we need to point it at some other "forwarder" we can use? As long as the Suse box has a DNS server, will emails go out OK even if the Domain Controller /Forwarder is down? It seems we need to get DNS from somewhere, and that we can't if the Windows domain controller is out.