We all got through the anticlimactic Y2K bug 22 years ago, and the next digital calendar crisis isn't expected until 2038 (Unix epoch), but... apparently Microsoft Exchange has a Y2k22 bug, which prevents email from being delivered until sysadmins apply a manual fix. Just what they wanted to hear on a holiday weekend.
Apparently Exchange is using a funny string representation of dates and then trying to convert that string to a numeric format, and with the bump in year it now doesn't fit into a long. Really, I'm not making this up. Why they don't use standard date formatting, I don't know. I don't know much about how Exchange is put together.
This linked Reddit post, which has had several updates, includes this:
Interestingly, this fix includes a change to the format of the problematic update version number; the version number now starts with “21” again, to stay within the limits of the ‘long’ data type, for example: “2112330001”. So, Happy December 33, 2021!