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)
.....

The error is related to a wrong path (/usr/share/sendmail-cf) in several config files in /etc/mail.
To solve identify all the config files with the wrong line.

grep -R sendmail-cf /etc/mail

After that you can fix the places it shows up with the correct path /usr/share/sendmail/cf.

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