If your company uses Office 365, these guys have a plugin that I think parses the HTML website to get your mail (and calendar!) into Thunderbird: https://www.beonex.com/owl/ Just this week I gave them 10 Euros for the addon because my company refuses to enable IMAP for Office 365. I'm not affiliated with them, but I've been using the Tbird addon for a few weeks and it works perfectly. The license is per-year, though…
Did you get this extension audited by your security team? It sounds insane to me that you’re bypassing IMAP restrictions, with a plug-in that monitors and parses the entire O365 website…
It’s like how having super draconian password reset and complexity requirements ends up being less secure because users will start writing their impossible-to-remember passwords on post-it notes.