A: Hey,
Your email signature includes links to images that you upload, banners, etc.
Without a custom domain, we host these assets (links) using our domain (s).
With the custom domain (CNAME) feature, the links in your email signature can now be branded with your domain. This is not only nice to have, but it also improves email deliverability. By replacing all links in your email with your domain, it increases trust and boosts deliverability.