Yup, in my hypothetical example, at some point "microsoft-teams.com" was registered by Microsoft. At that time, some engineer deployed something that involved t

Yup, in my hypothetical example, at some point "microsoft-teams.com" was registered by Microsoft. At that time, some engineer deployed something that involved the CNAME. Over time, "microsoft-teams.com" was moved elsewhere and the domain became unregistered, but the engineer maybe forgot or left the team, and nobody remembered that there's this out of date "abcde.teams.microsoft.com" DNS record just sitting there. Microsoft has a lot of these, just random Microsoft-ish domains that were used at one point or another. It's a problem because it makes it harder to look at the domain name as a sanity check against phishing.