You are only allowed to send direct email marketing to individuals who have agreed to receive it from you by actively opting in. It is not sufficient simply to provide an opt-out. However, if you obtained their details in the course of making a sale the rules are different. You are allowed to continue communicating with them until they tell you otherwise, provided there is a free method of opting out each time you send them an email. You can use email for the opt-out.
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