I can receive emails but I cannot send emails with Thunderbird. When I try to send an email I get the error message: "Login to server smtp.office365.com with username info@mybusiness.com (not my real email address) failed". When I click on "Enter new password" nothing happens, the Window to enter the new password doesn't pop up just the same error message as above appears. Already tried everything I found in the forum as I see I am not the only one with this problem but nothing helped so far. Changed from OAuth2 to Normal password, deleted the OAuth and SMTP lines in Settings-Security-Saved Passwords but no difference... My system: Windows: 11 Home 10022631 Build 22631 (all updates) Thunderbird Version: 115.51 (latest version) Firewall/Antivirus: Windows Defender (all updates) 1.401.1565.0 Mail provider: Office 365 business (business email address: info@mybusiness.com) SMTP Settings: Description: name@mybusiness.com Server smtp.office365.com Port: 587 Security: STARTTLS Auth method: OAuth2 User name: name@mybusiness.com (see attachment) I hope someone can help me otherwise I have to use Outlook in which btw I can send emails and as well with my Gmail mail client so the problem is definitely with Thunderbird. Thanks for any help!