We just signed up for a Microsoft email account this weekend. Preferring to use TB, everything seemed ok as I was able to receive emails just fine, but upon trying to send emails, I continue to receive an error message saying "Login to server smtp.office365.com with username tom@callablefirst.com failed". I have gone through many different troubleshooting techniques I read about in the community and here is a checklist of things tried: 1. Checked that IMAP is toggled on in 365 admin 2. Checked that TB is accepting cookies and no exceptions are listed 3. Tried changing SMTP server to recommended instructions from Microsoft and verified all settings are OAuth2 4. Enabled 2F Authentication 5. Used config. edit to clear out all existing OAuth2.scope files I have downloaded a different email client- eM client and everything works fine sending emails from that end so I am convinced this has nothing to do with my password being entered incorrectly, but some unknown conflict that isn't getting resolved between TB and the 365 account. I prefer using TB but am getting to the point where this is taking a lot of time away from other business activities that need to get done. I have my marketing guy trying to remotely help figure things out, too, but he is at a loss as well. Let me know if you have any ideas, thanks, much!