In general a software package named sendmail will reside under /software/sendmail (which will be a symbolic link to a particular version. Information from man sendmail-config, run on the specific machines in question, will take precedence over anything on these TWiki pages.
The sendmail package has had different versions, found under /software/sendmail-_version_.
In vendor version 8.13, two different xhier versions of the package exist, sendmail-8.13, and sendmail-client-8.13.
Generally, sendmail-8.13 must be used if the machine is to allow SMTP connections by other machines, otherwise sendmail-client-8.13 should be used. More rigorously, any machine which does not accept SMTP connections and uses another machine as a mail_hub must use sendmail-client-8.13.
-- AdrianPepper - 28 Oct 2008