I get lots of questions about how to manage changes to the links used within email. This can happen with a business name changes, a business acquisition or just a rebranding process.
When customers change out the branding on a tracking link or a landing page this means setting up a new subdomain and pointing their domain to the Marketo CNAME.
I recommend is setting up the CNAME on the new domain and leaving the same CNAME in place for the old domain for at least 3-6 months. This ensures that any older links that may be activated will continue to work as your recipients may dig up an old email to review content.