Optimal solution to opt out users from non marketing emails?

Hi!

Anyone have ideas on the best solution to opt out users from non marketing emails?

We have a Salesforce sync and a field indicating whether or not the user is opted in to marketing emails only.

When we get a request to keep a user in marketing emails but opt them out of service/transactional ones, what's the best way to handle this?

Create another field for non marketing emails opt out?

Maintain a separate opt out list for non marketing emails?

etc.

Thank you for your help!

Emily