How a Recipient Can Opt Out of Receiving Text Messages
Each person can change their preferences for communication at any time.
The recipient can text STOP to the same receiving phone number to opt out of text messages at any time. You will receive a text message that states: "You will no longer receive communication from _______________ via text message. Text START or UNSTOP to opt back in."
How an Admin Can Opt Out Someone Else from Receiving Text Messages
You will need Full SMS permission to complete this task.
From the top Settings Cog Menu:
Communication > Text Messages > Logs tab > Opt Outs sub button.
Then, enter the phone number you want to Opt Out of receiving text messages.
Other Helpful Links:
How do I send a text message?
How do I set up keyword text messaging?