Note by @fastfinge

Hey #xmpp and #jabber experts on Mastodon: my XMPP server is im.interfree.ca, and so my JID is fastfinge@im.interfree.ca. However, I would like to alias my JID to fastfinge@interfree.ca. That way my email, jabber, and fediverse id's are all the same. I control the DNS on the entire domain. How can I do this? A quick search isn't finding me a list of clear and straightforward steps.