Thunderbird calendar sync fail caused by lack of "www"

When a "Synced Calendar URL" from the church's website is used when trying to create a calendar subscription in Thunderbird 140, it fails with "Could not find calendars at this location".
Not seeing anything about it here, I dug in and figured out the problem, and filed a support ticket to request a fix.

The cause of the problem is that the published URLs, which lack the initial "www", return a 301 error (permanent redirect) to the same address but under the"www" subdomain.
Some calendar clients will follow the redirect; others, like T-bird, will fail.

Until the URLs on the website are fixed, if you have this problem, just add the "www." yourself.

cboling wrote: Tue Sep 22, 2026 12:03 am Some calendar clients will follow the redirect; others, like T-bird, will fail.

I don't know much about the calendar subscription functionality, but HTTP 301 redirects should be honored. Did you also file a bug with Thunderbird?

Thanks for sharing the results of your "digging" into it.

I saw multiple Mozilla tickets already addressing the problem; apparently MS Office 365 calendar servers have begun exhibiting a similar behavior.