Currently, the mailx device must be manually added to the device tree.
In the future, the Wizard > Devices > Core page in the web admin, will provide a place where you can quickly enable/disable mailx, but for now:
* Go to the web admin,
* Advanced > Configuration > Devices, select the CORE device
*click add child device, on the right.
* in the device template drop down, find and select the Mailx device.
* select Pick Device template.
The device and its associated packages and driver will then be installed.
You can then interact with the device in scenarios and events as needed.