This is not a question, this is to provide a solution to a problem that caused me a lot of headaches I was not able to use smtp send with an MS365 account from thunderbird (and I suspect other people have this problem). There was always an authentication issue. This is what I did to get things working. This is for MS365 accounts - this may not work with hotmail or the other free MS accounts, I'm sure there are other useful tips for those accounts. 1. Firstly, MS365 defaults on an organisation level to not using OATH2 on SMTP for users. Get your MS365 admin to do the following: a) Go to MS365 admin centre (not the exchange admin centre) b) Click on Users->Active Users->your user name (side window pops up) c) Click on manage email apps (under Email apps) d) Enable the Authenticated SMTP (this is on a per user basis) 2. The next trick which is not clear is that editing the server settings in thunderbird do not seem to take affect until thunderbird is restarted. a) Setup thunderbird account in the usual manner - this is fairly straight forward so won't be repeated here. I selected the IMAP settings which appeared at the top of the thunderbird autoconfiguration list. b) The outgoing server settings should look like this: Description: <whatever you like, but email address would make sense> Server name: smtp.office365.com Port: 587 Connection Security: STARTTLS User Name: full email address Authentication Method: OAuth2 c) Restart thunderbird. 3. Another issue with sending to gmail addresses is gmail seems to suspect a typical test message is spam and gets lost in the ether. To get around this, I set up a meaningful signature (which you probably would want anyway with an MS365 account). This worked for me, I hope someone else finds it useful.