If you are using ActiveTrail in conjunction with Remarkety, you can now use their webhooks feature in order to ensure that people who unsubscribe from ActiveTrail are also unsubscribed from Remarkety.
Here's how to set this up:
1. You'll need the webhook URL, which can be found under Account Settings -> Services and Integrations:
2. In your ActiveTrail account, go to: More -> Integrations -> API -> Apps -> Webhooks tab. Paste the URL that you got from Remarkety into the URL field (both in Contact Changes and in Contact Manual Changes), click "Add URL", and make sure that the Enabled checkbox is checked.
Make sure to initially sync the existing unsubscribe list by exporting it from ActiveTrail and importing into Remarkety.