KMail not receiving messages

I installed Leap 16.0, and KMail is not working. I got a few messages while my system was down, and KMail downloaded them when I launched it the first time. Then it stopped downloading messages entirely. When I noticed it was happening, I tried “akonadictl restart,” and didn’t see any errors in the output. However, I did get four notifications in the system tray:

Resource Local Folders is broken.
Unable to start

Resource *****.net (dan) is broken.
Unable to start.

Resource *****.org (webmaster) is broken.
Unable to start.

Resource Google Mail (*****) is broken.
Unable to start.

(I redacted some information.) How can I fix those resources so they work as they did at the beginning, and how can I keep them from silently breaking again? I missed an important email because I didn’t realize KMail had stopped receiving.

I tried “akonadictl fsck; akonadictl vacuum” and restarted it again with the same results. KMail reports that “Local Folders” is “Ready,” and the others are “Offline.” (“Work Offline” is not selected.)