Using Sendmail usually when you need to “recompile” the config file you have to launch the next command.
make -C /etc/mail/
In Debian you can get the next error.
make: Entering directory '/etc/mail' Updating databases ... Reading configuration from /etc/mail/sendmail.conf. Validating configuration. Creating /etc/mail/databases... Could not open /usr/share/sendmail-cf/m4/cf.m4(No such file or directory) .....