I have just migrated to Thunderbird from Outlook 2013. I've added my Exchange account and Thunderbird has successfully synced all my emails past and present, and is working perfectly on the Mail side of things. However, the Calendar is completely empty. It hasn't imported any of my events, and when I create a new one this doesn't appear in my other synced apps (e.g. on my phone etc.). If I try to add a new network calendar with the same account details as my email account, it says the credentials are not accepted. I tried downloading the TBSync add-in and Exchange server extension but got the same errors. I've tried creating an app password from my Microsoft account but this didn't work either. I must be missing something very simple here. I'm really not sure why TB didn't simply sync my calendar events at time it set up the email account?