Advanced Opt-Out for Messaging Services
Messaging Services customers can customize opt-in/out keywords and replies by using the Advanced Opt-Out feature
STOP, STOPALL, UNSUBSCRIBE, CANCEL, END, or QUIT
Recipients can send words such as STOP, STOPALL, UNSUBSCRIBE... to opt-out. However, sending Please Stop or Stop please does not work.
This feature works for the most recent sending number that the contact received the message from. If you're sending from different numbers, only the reply to the most recent one will work.
START, YES, and UNSTOP
These replies can help in receiving the messages or re-subscribing. To re-subscribe, only START and UNSTOP work.
HELP and INFO
These replies send basic information on how to opt-out or opt-in again. It's recommended to add the business name in the customized advanced replies.
If you use messaging services to send SMS, any STOP keyword reply will opt out the contact from all the phone numbers pools. On the other hand, any START keyword reply will have them active on all the phone number pools.
By default, Twilio will not handle opt-out, opt-in, or help keywords for shortcode numbers, unless the shortcode has been added to a Messaging Service.