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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.
Additional Resources about Landing Pages (Personalization) - Marketo Docs - Product Docs