The template
Subject: Updated link for {product} in your post
Hi {first name},
Thanks for linking to {product} in your post on {topic}. We recently {moved to a new domain / reorganised our site}, so the link under "{section}" now {redirects / goes to a 404}.
The current page is {new URL}. If you get a moment to update it, readers will land in the right place.
Thanks again,
{your first name}