You can uninstall or removes an installed dhis-mx-sendmail-engine package itself from Ubuntu 16.10 (Yakkety Yak) through the terminal,
$ sudo apt-get remove dhis-mx-sendmail-engine
If you would like to remove dhis-mx-sendmail-engine and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove dhis-mx-sendmail-engine
If you use with purge options to dhis-mx-sendmail-engine package all the configuration and dependent packages will be removed.
$ sudo apt-get purge dhis-mx-sendmail-engine
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove dhis-mx-sendmail-engine