Looking around on the community it doesn't look like it's possible to have a separate Unsubscribe link for each branding domain, is that right?
Comprehensive Multi-Domain management (I'm referencing number 6 under "What's Really Missing")
Is there no variable that can be used in the in the Unsubscribe HTML in the Email Admin section that will change dynamically based on the chosen branding domain?
I had an idea for a workaround, where perhaps the user can be redirected to the right unsubscribe page based on what the document.referrer value is. I assume this would work as long as the user were being referred by the email tracking server. Let me know if this sounds risky.
Another alternative is, for all emails that are not using the default branding domain, to make them operational emails to hide the default Unsubscribe HTML and to add the unsubscribe link directly to the template. Is this the best option for now?