The "soft opt-in" rule is an exception to the general requirement of obtaining consent before sending electronic mail marketing to individuals. It applies when the following conditions are met12:
the sender has obtained the contact details of the recipient in the context of the sale or negotiations for the sale of a product or service to that recipient; the sender only sends direct marketing relating to its own similar products or services; and the recipient has been given a simple opportunity to refuse or opt out of the marketing, both when the details were initially collected and in every subsequent message.
The option B matches these conditions, as it implies that the individual has shown an interest in buying a product from the sender, and that the sender can use the individual's details to send marketing about similar products, as long as the individual can easily opt out. The other options do not qualify for the "soft opt-in" rule, as they either involve no consent, no prior relationship, or no opt-out mechanism. Reference: Electronic mail marketing | ICO, Direct marketing rules and exceptions under the GDPR