We implemented this the same way we had done it on Class2Go:

* **Course emails** take you to the site.  Since these are transactional emails (you've opted into a course) then we feel that's fine.  That's the feature implemented here.

* **List emails** are using the same mailing backend, but sent to arbitrary mailing lists.  This is what we us for sending out mass mailings, usually commercial mails.  You explicitly have to upload a CSV with {name,email} and then we'll send directly to them.  And for those we will have a one-click unsub, just hitting an endpoint with an opaque userid.  Since those are unsolicited commercial email (no opt in has taken place) that meets the one-click criteria.

This is what's captured in the [stories](https://docs.google.com/document/d/1s1Jq1SId-aeDV1XlW3Qoq9L9R0-UTkrO6XLqiTa0nRU/edit) for this feature.  

I guess we could have done both with the token mechanism, but instead of choosing to rethink the feature, the original requirements we had were "do what Class2Go did" so that's what @kluo did.