DNS and ZMailer

ZMailer: The Manual; v1.99.20
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# Chapter 9. DNS and ZMailer

The cornerstone of everything in busy Internet email routing is a properly working DNS server, and a modern resolver library. If you use the BIND nameserver, you should be using a recent version, at least BIND 4.8. (As of this writing, bind is on version 8.1.2)

You can get improved DNS performance by installing local named(8), which does cache replies, including negative replies.

For the file `/etc/resolv.conf`:

      domain     your.domain
      nameserver 127.0.0.1
      nameserver (some other server)

For the local nameserver daemon (named(8)) you should have at least following type of configuration:

    For 4.* series:  /etc/named.boot
      forwarders 10.12.34.56  10.45.67.89
      options forward-only

    For 8.* series:  /etc/named.conf
      options {
          forward only;
          forwarders {
                 10.12.34.56;
                 10.45.67.89;
          };
      };

which means that all the queries are attempted to be resolved by the servers at IP addresses 10.12.34.56 and 10.45.67.89, and both the local server, and remote servers will cache DNS responses.

For Solaris, Linux, and some other environments you propably have file `/etc/nsswitch.conf`. There the interesting line is one referring with "hosts:" tag. In most cases the default setup assumes you will use e.g. NIS(+) in the system overriding DNS and/or local files. In general that is quite bad thing to do — especially for DNS intensive application, like mailers... Suggested value:

      hosts: files dns

At DEC Tru64 there is another file with same purpose as `nsswitch.conf`, it is: `/etc/svc.conf`.

At Solaris 2.6 (and after?) there is also a ``nscd'' daemon (name service cache daemon), which has appeared at times to harm DNS lookup intensive systems. At its configuration file `/etc/nscd.conf`:

         enable-cache    hosts   no

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