The addon is called : Owl for Exchange 0.7.9.4 https://addons.thunderbird.net/en-us/thunderbird/addon/owl-for-exchange/ The home page is : https://www.beonex.com/owl/ ''The addon allows you to use your Exchange and Office365 email account using Outlook Web Access (OWA) with Thunderbird. After setup, your account should appear in Thunderbird just like the other accounts. You can read and write emails with your Exchange account.'' ''This is a paid addon. See the website https://www.beonex.com/owl/ for prices. The first month is free, so that you can test it and see whether you like it.'' ''The developers of this addon have contributed many parts to Thunderbird as Open Source, and they are active around Thunderbird and its predecessor since many years, since almost 20 years. This is how we're earning our living.'' Insalled addons are located here: * Menu icon > Addons and Themes > Extensions.