Many versions of Sendmail do not support the mailertable mechanism. This
is a compile time option and few Linux distributions have chosen to
include this feature. In the "basic information" screen, there is a
checkbox to enable support for it (special routing database). If you
enter some routing in the table, Linuxconf will warn you if the feature
has not been selected. Once you have selected the feature (the checkbox),
you must regenerate the sendmail.cf file.
If your sendmail fails to start after that, check the error logs
in /var/log. Your sendmail may not be configured to support
the mailertable concept.