See https://github.com/guderkar/MExInt/blob/master/README.md For several years I have had no luck adding Microsoft Exchange accounts (in corporate medical institutions) that did not have clearly visible IMAP/POP3 configurations. That I would even have to log in to the Outlook Exchange Web Services and noodle around in the settings was probably more than the average Thunderbird user had time to try. I tried DavMail but was completely flummoxed by it and could not get it to work. This was generally the principal direction I received from searches and forums online. That, and using ExQuilla, which costs $10/year to add something that seemed relatively straightforward to the free and open-source repository that is Thunderbird. At a certain point (about a year ago), I just gave up, so until today I had been using emClient for my Exchange only accounts, even though this is touted as a service that Thunderbird should typically handle. When I set up guderkar's app, which simply required that a couple of permutations in standard questions (basic or NTLM authentication), (certificate or no certificate), and a standard server name ("email domain"/EWS/Exchange.asmx), my e-mail started downloading. And I can send! I'm overjoyed. If this is incorporated into Thunderbird or made more widely available, I think it will increase the utility of the program, especially to users in Enterprise settings, where OWS/EWS/OWA is standard.