How does unsubscribing work?
Here's a brief overview of how unsubscribing works in MageMail.
Customers can unsubscribe by clicking the unsubscribe link in the footer of any email that they receive. This will unsubscribe them from all MageMail emails (except for order confirmation emails - those don't respect any unsubscribe preferences).
By default, it will not unsubscribe them from the Magento newsletter, but we can enable that for you if you're interested.
If you have the Mailchimp bidirectional sync enabled, that unsubscribe will also be sent up to your Mailchimp newsletter list, so that they'll be unsubscribed from your Mailchimp newsletter.
If you use something other than Mailchimp to send your newsletters, we'll need to build a custom integration to sync up the unsubscribes. Get in touch with us if you're interested in that.
On the other hand, if someone unsubscribes from your Mailchimp newsletter, we will import that unsubscribe into MageMail and not send them any future MageMail emails.
While MageMail emails are not double opt-in, they're based on the principle of contacting people with whom you have a pre-existing business relationship. While I am not a lawyer and this is not legal advice, there are some notes on legal issues that you can review if you're interested.