A kind reader pointed out to me that my Atom feed was incorrect. There were two
problems. First, I was specifying an incorrect URL in the feed’s
<link rel="self"> – it was pointing to a nonexistant feed.xml file. Second, I was
<link> tag from the entries entirely.
Thunderbird didn’t like this. With no
<link> for an entry, it would show the
<link> in it’s UI. And that link left users at a 404 page.
I pushed a fix this morning. You might have to refresh or resubscribe to pick up the changes.