In true EFF fashion. Their second server / backup MX is hosted at some other smaller company so things could be worse, at least their MX as a non Microsoft alternative.
Either way I can get this, they most likely have hundreds of people using Microsoft products, like Office 365, and Outlook’s compatibility with IMAP is a joke. They most likely also don’t want to run a serious in-house email infraestruture capable of handling that load. All reasons might have driven them to Microsoft / O365.
This is usually what happens, when your company is big you can’t make it with open-source without tons of extra costs and complexities. Sad but true.
Hell, even SMB really can’t easily/cost-effectively run without MS.
Sad, but true.