To enable this, open the MightyText Web App, and under Settings, and enable the Delete Messages on Phone setting.
If you're running Android 5.0 or higher, you will need to install our SMS app on phones, SimplyText, and set it to be the default SMS app on your phone in order for delete sync to work properly. (see Note below).
We only support deleting individual SMS at this time. Threads will NOT be deleted on your phone if you delete a thread in MightyText.
Note: MightyText requires SimplyText to be the default SMS app on your phone for this to work because only the default app has permission to make changes to the SMS database on the phone in Android 5.0 and above. (This is a restriction on the Android platform).