This depends on how you access Donky.
If you are using Campaign Builder to manage and deploy your Push, Rich and Chat campaigns, you are able to take advantage of an embedded feature that handles this for you. Users can simply send the word “STOP” as an inbound to one of your app identities. This will be automatically processed by Campaign Builder, opting the user out of receiving any further messages from you at all.
In addition to the industry best practice of opting out users on receiving a "stop" message, in Campaign Builder you can setup custom rules to opt out users from future communications based on other criteria or keywords.
If you choose to integrate the Donky network with your own systems, we are not able to offer you this turnkey solution and you will need to manage this process.