It's shameful how far we've gone down this path. My university is using Microsoft Exchange and they refuse to allow IMAP access even with Oauth2, only allowing you to use proprietary protocols. So far I've only seen Evolution and Thunderbird working (with a paid plugin for the latter). I think it's a means to exert control on your email usage. For example, most sane clients do not show images by default, which prevents various types of tracking pixels from working, whereas Outlook doesn't do this afaik.