Thanks to Ben and Chad for helpful suggestions along these lines:

>>>>> "CCW" == Chad C Walstrom <chewie at wookimus.net> writes:

    CCW> On Wed, Jan 09, 2002 at 09:07:16AM -0600, Robert P. Goldman
    CCW> wrote:
    >> I have a small home network behind a firewall, so small that I
    >> haven't thought it worth having a name server.  My desktop
    >> machine runs sendmail (I know, I should probably change to
    >> qmail or postfix, but that seems like a lot of effort for low
    >> payoff on a single-user machine) and keeps putting into my
    >> system logs a record that a gethostbyaddr call on its own
    >> (unroutable) address has failed.

    CCW> Do you have your FQDN for your local host in /etc/hosts?  If
    CCW> you do, you shouldn't have problems.  Otherwise, consult the
    CCW> Sendmail manual and shut off DNS lookups.  Look for a
    CCW> "Definition" string.

Sorry.  I should have pointed out that I have a small network behind a
firewall, and the firewall serves up the DNS addresses to the machines
behind the firewall using DHCP.  So I'm not sure how to use a hosts
file to keep track of addresses.  I hate to go to the trouble of
setting up a DNS server for what seems like a trivial net.  Is there
an alternative?

    CCW> With regards to a name server, if you have a small enough
    CCW> network, you really don't need one.  "In the olden days"
    CCW> people distributed an /etc/hosts file to all the machines on
    CCW> the network.  This doesn't scale too well, but it works great
    CCW> in small environments.

    CCW> As far as running this or that email server, it largely
    CCW> doesn't matter.  You're behind a firewall.  You should be
    CCW> able to use your ISP's SMTP server as a "SmartHost" and
    CCW> configure your local Sendmail as a "null client".  As a null
    CCW> client, it'll defer DNS lookups to the upstream relay agent.

    CCW> Another term for a null client is a Mail Sending Agent (MSA).
    CCW> Mail Delivery Agent (MDA) applies to the local mailer,
    CCW> delivering email to local user accounts.  The Mail Transport
    CCW> Agent (MTA) refers to an MSA+MDA.

    CCW> If all you need is a MSA, look into ssmtp[1].  It's a very
    CCW> small, simple MSA that has no local delivery capabilities and
    CCW> does not implement a local SMTP server.  It doesn't open up a
    CCW> local port 25 to accept connections at all.  It simply acts
    CCW> as a replacement for the basic sendmail commands to send
    CCW> email.  It may not be the most elegant solution, but it works
    CCW> well.

But don't I want local delivery capabilities so that, for example, my
scripts can send me email about how they worked?  

You're right --- my sendmail just does two things:

1.  routes all the email for the various script outputs to me and 

2.  uses a smart host for any addresses not on my box.

Thanks,
R