MobileX can be added as an Outlook Add-in to Outlook 365, Outlook 2016, Outlook for IOS and Outlook for Android.
Installation of MobileX is covered in Installation Section.
After Installing MobileX, you will see the following Icons based on your device:
For Outlook 2016 (windows):
For Outlook 2016 (Mac):
For Outlook Web Access (OWA) select an email and the icon will appear beside Reply All: