As a default, when you created an SMS Central account we automatically created an Unsubscribe Rule for you.
This rule has the keyword STOP (so any contacts sending inbound messages containing that word will be automatically unsubscribed).
You can add more keywords (or change them) by following these steps:
#1 Go to Settings > Rules & Triggers.
#2 Click on the 'Unsubscribe' rule from your list.
#3 Add as many keywords as you like in keyword box. If you ONLY want to unsubscribe messages that begin with these words (not just contain them) you should select "Begins with).
#4 Click Save Rule.
If you happen to have deleted the default unsubscribe rule, then do the following:
Go to Settings > Rules and Triggers and create a rule.
When setting up, select “receiving SMS”.
You can select to unsubscribe contacts only if their SMS is coming to Shared Numbers or a particular dedicated number of yours. If you want to unsubscribe contacts regardless of the number they are being sent to, pick “Any Number”.
You can then enter as many keywords as you please if you only want to forward particular SMS depending on the keyword(s) they contain. If you would like all incoming SMS contacts to be unsubscribed regardless of keywords, leave these boxes blank.
Go to the next step, and select “Unsubscribe the matching contact”.
Click Save Rule and… you are one step closer to compliance heaven!