The "Local command shell" option controls what shell will be used for delivery to external command. By default, external commands are executed directly; commands are given to given to /bin/sh only when they contain shell meta characters or shell built-in commands. This option sets the "local_command_shell" postfix variable.
Specify a different shell when you need more control over what programs can be run from e.g. .forward files.
"sendmail's restricted shell" (smrsh) is what most people will use (smrsh is part of recent sendmail distributions)
Note: when a shell is specified, it is invoked even when the command contains no shell built-in commands or meta characters.
The "Forward path" option specifies a search list. The first file that is found is used.
The following expansions are done on forward_path: $user (recipient username), $shell (recipient shell), $home (recipient home directory), $recipient (full recipient address), $extension (recipient address extension), $domain (recipient domain), $local (entire recipient localpart), $recipient_delimiter. Specify ${name?value} or ${name:value} to expand value only when $name does (does not) exist. This option sets the "forward_path" postfix variable.
The "Allow mail to commands" option restricts mail delivery to external commands. The default is to disallow delivery to "|command" in :include: files. This option sets the "allow_mail_to_command" postfix variable.
The "Allow mail to files" option restricts mail delivery to external file. The default is to disallow delivery to /file/name in :include: files. This option sets the "allow_mail_to_files" postfix variable.