Before you install this software
JMailQ works at a low level within the Joomla system. Every Joomla installation is different and it is impossible to pre-test this software against every possible configuration. Therefore it is imperative you do initial testing on a sandbox version of your site to ensure there are no incompatibilities with other components you have installed.
It is also imperative you back up your site prior to installing this software. We recommend using Akeeba Backup (https://www.akeebabackup.com/) a free and excellent backup component. Copy the backup to a safe place (outside of your Joomla installation) before installing JMailQ. In this way if things go wrong you can restore your site to its state before the installation of JMailQ.