Mac OS X 10.3 (Panther) ships with the postfix Mail Transport Agent (MTA) by default. To use Sendmail instead, compile it from source. Older versions of Mac OS X shipped with more or less misconfigured versions of Sendmail, as documented below.
Sendmail in 10.2 is very similar to the one shipped with 10.1.5. However, the default configuration files and crontab setup are different, so the older notes for 10.1.5 are not perfect.
These pages do not cover any versions of sendmail that ship with Mac OS X Server; I only have access to the regular Mac OS X release. To determine what the version of Sendmail is and the release of OS X, use the following commands.
$ sendmail -d0 < /dev/null | grep -i vers
Version 8.12.11
$ sw_vers
ProductName: Mac OS X
ProductVersion: 10.3.2
BuildVersion: 7D24