Technically, since there is a durable unsubscribe in Marketo, what you could do in your Smart Campaign flow for purging is to Change Data Value of Unsubscribed to TRUE before you remove the person from the database. This way, if the lead was to come back into Marketo, they wouldn't receive any emails. Since there isn't a sync, you would have to manually do this within Salesforce too. Is there a way for you to mark all of these contacts as inactive within SFDC as well? That way, you would be able to filter out those that are inactive from any list exports in Salesforce, so that you wouldn't have those enter back into the database.
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