People can opt-out from your SMS marketing campaigns by utilizing the free, randomly generated unsubscribe link provided when you create an account.
When a user opts out of receiving SMS messages, their phone number is automatically removed from all of your contact lists and added to your opt-out list. For future usage, this opt-out list can be accessed, changed, updated, and exported.
Until the sender chooses to opt back in, any texts sent to this number from your account will be blocked. If you accidentally upload the number to your contact groups again, the system will remove it for you, preserving the opt-out.