A blacklist is a listing of message recipients that chose to opt-out of getting any SMS messages from the business in the future. Blacklists are widely needed for promotional campaigns where companies give an alternative to the end customer so he or she does not get messages irrelevant to them. Having an opt-out inside every SMS message is required by law in some countries.
Apart from the blacklists, owned by every company for their messaging campaigns, there is also a DND or Do Not Disturb option.
Those listings are used by the Mobile Network Operators to secure their subscribers. If one of their users decides to be on the Do Not Disturb list, they will not receive advertising messages, no matter if they’re subscribed to a newsletter or not. This is a technique used by MNOs to challenge churn rate and users spamming.
There are some apps have the opt-out by default for all messages received by their users e.g. Viber .