Why did my emails go back to Sent via Jounce?

Nothing stopped. If Jounce can no longer authenticate your domain, it sends your emails from your address at send.jouncemail.com instead. That way a send never waits on your DNS. The From card reads Sent via Jounce again, and replies still reach the workspace owner’s sign-in email.

Two things it can be

The records went away. Someone edited the domain’s DNS or moved it to another provider, or the domain’s registration lapsed.

The Your own sending domain card reads Not authenticated and lists the records again. Put them back exactly as shown, then select Verify. If the badge doesn’t recover after a few hours, remove the domain and add it again. Why does my domain say Not authenticated? has the steps.

Someone removed the domain. An admin or a manager selected Remove domain. The card is back to its Domain field with no badge at all. Ask an admin or a manager; adding the domain again puts it back.

How Jounce noticed

Jounce checks an authenticated domain on its own, not only while you set it up. A brief hiccup in that check changes nothing. Only a clear failure turns the badge to Not authenticated.