wget http://www.acme.com/software/mini_sendmail/mini_sendmail-1.3.6.tar.gz
tar zxvf mini_sendmail-1.3.6.tar.gz
cd mini_sendmail-1.3.6/
make
cp mini_sendmail /usr/local/bin
gzip mini_sendmail.8
cp mini_sendmail.8.gz /usr/local/share/man/man8

configure a minimal smtp server so automated emails (cron etc) can be sent

apt -y install exim4-daemon-light mailutils sed -i "s|dc_eximconfig_configtype='local'|dc_eximconfig_configtype='internet'|g" /etc/exim4/update-exim4.conf.conf /usr/sbin/update-exim4.conf systemctl restart exim4