DND Preference End User Options Explained
The activation of DND on a phone number under TRAI guidelines is not binary, i.e. it is not just DND Active/Inactive. There are preferences that the end-user can set for receiving messages based on the category of the message, while DND is enabled for them. If the end user chooses to receive SMS on select categories or for partially blocked registration, they can send SMS in this format: START