Most operating systems provide a program to handle local delivery of mail. Typical programs for many of the major variants of Unix are already built into the sendmail binary.
In , it is necessary to explicitly define the appropriate local mailer since a local delivery program is not necessarily present in the distribution you've installed. This is done by specifying LOCAL_MAILER_DEF in the sendmail.m4 file.
For example, to have the commonly used deliver program provide this service, you would set LOCAL_MAILER_DEF to mailers.linux.
The following file should then be installed as mailers.linux in the directory pointed to by LIBDIR. It explicitly defines the deliver program in the internal Mlocal mailer with the proper parameters to result in sendmail correctly delivering mail targeted for the local system. Unless you are a sendmail expert, you probably do not want to alter the following example.
There is a also built-in default for deliver in the Sendmail.mc file that gets included into the sendmail.cf file. To specify it, you would not use the mailers.linux file and would instead define the following in your sendmail.m4 file:
Unfortunately, Sendmail.mc assumes deliver is installed in /bin, which is not the case with Slackware1.1.1 (which installs it in /usr/bin). In that case you'd need to either fake it with a link or rebuild deliver from sources so that it resides in /bin.