Many, many places (even academia, not just businesses) only allow Outlook to be used as an email client "for security" these days -- they actually go out of their way to disable POP and IMAP access and even use Microsoft's authentication system to get access. I've been using email for close to 40 years at this point, and I actually did use Emacs as my e-mail client in the 1990s, but that hasn't been possible anywhere I've worked for close to two decades at this point.

Thunderbird supports what Microsoft call "Modern Authentication" for MS365. I'm not sure if that's enough, or if the administrator can still block Thunderbird.

Unfortunately, emails (at least in my context) are rich text, and they pretty frequently include images that I care about. I don't think gnus can handle that, given that it looks CLI-only.

But also, it looks like I'd have to do some substantial elisp work to get filtering, etc. working. This is starting to sound like way more work than hitting Ignore on a Slack thread. Maybe it's great once you get it set up, and assuming nobody sends you rich text where you care about the formatting?