Most of us probably rely on sendmail emulation from Postfix or some other MTA. But if you need to use Webmin’s sendmail module and encounter errors while setting it up, the installation may not be complete.
For errors about a missing /etc/mail/sendmail.cf file and/or m4 command, verify that the following package is installed after installing Webmin’s module.
Name : sendmail-cf Version : 8.15.2 Release : 32.el8 Architecture : noarch Size : 198 k Source : sendmail-8.15.2-32.el8.src.rpm Repository : AppStream Summary : The files needed to reconfigure Sendmail URL : http://www.sendmail.org/ License : Sendmail Description : This package includes the configuration files you need to : generate the sendmail.cf file distributed with the sendmail : package. You will need the sendmail-cf package if you ever need : to reconfigure and rebuild your sendmail.cf file.
dnf install sendmail-cf
actually installs two missing pieces.
(1/2): m4-1.4.18-7.el8.x86_64.rpm (2/2): sendmail-cf-8.15.2-32.el8.noarch.rpm