Install lsb-invalid-mta by entering the following commands in the terminal:
sudo apt update sudo apt install lsb-invalid-mta
Description:
Linux Standard Base sendmail dummy
The Linux Standard Base (http://www.linuxbase.org/) is a standard core system that third-party applications written for Linux can depend upon. . This package contains nothing else than a fake /usr/sbin/sendmail command to fulfill the LSB's requirement of providing this command without requiring an MTA to get installed, which once introduces a daemon which can cause security problems and second, users get asked questions about how they want their MTA configured when in reality they simply wanted to install a desktop application or a printer driver, but the dependency on LSB compliance pulls in an MTA with the installation. . The LSB requirement on /usr/sbin/sendmail comes from old times where Linux and Unix machines had all fixed IPs and did server tasks in data centers. Today's typical desktop Linux machines do not do local e-mail any more as users use external e-mail services. . The /usr/sbin/sendmail always exits with exit status -1 (255) and sends a warning message to stderr, so that if a program actually tries to send e-mail via the sendmail command the user gets note.
Homepage: https://wiki.linuxfoundation.org/lsb/start
Version: 9.20170808ubuntu1
Section: universe/misc