To be compliant with Anti-spam guidelines, and not send unwanted messages to your customers, you can use Subscription Management. SMS Subscription management protects your brand from accusations of spam or unethical practices.

There are 2 Opt-out Preferences: 

1. System-Wide Opt-out 

If a particular number is opted-out, then messages won’t be sent from any of the numbers (sender ids). 

2. Sender-ID wise Opt-out 

Subscription status would be based on a particular sender ID. Also, a user would be able to send a message using a different Sender ID. 

You can upload a list of contacts with the status of subscribe/unsubscribe or add a single contact at a time.