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. 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.