To subscribe or unsubscribe a buyer form a Mailing List, you will first need  one of the 3 integration that we have in our Add-on Marketplace:

After you have the integration made, in the Buyers app you will have the fields Buyer Type and Subscription Status. You can choose in which lists you want to subscribe the buyer in and after that hit Subscribe (you can enroll one buyer into multiple lists)

Subscribing a Buyer into Email Blast

Unsubscribing a Buyer from the Email Blast

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