Block Unsubscribing a contact will remove them from any Campaign they are on, it will prevent them from ever being emailed again, remove them from the Group/s they are in, and if you have the Email Opt Out sync to Salesforce turned on, it will mark them Email Opt Out in Salesforce.
Unsubscribing will remove the recipient from groups and fail any existing scheduled emails to the recipient. However, it will not prevent you from emailing them ever again and will not sync to Salesforce.
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