Hello, I am requesting assistance with a persistent issue in Thunderbird involving a Google Workspace (Gmail) account for my domain, dantanas.com. Incoming IMAP works correctly. However, outgoing SMTP authentication fails every time. Symptoms The Google OAuth login window never appears when Thunderbird attempts to authenticate SMTP. Sending mail produces the error: “Unable to authenticate to Outgoing server (SMTP). Please check the password and verify the authentication method.” IMAP works normally, but SMTP never prompts for OAuth authentication. Thunderbird also does not allow me to have a Junk/Spam folder for this account — the option appears disabled or unavailable. Current configuration Thunderbird is using SMTP Server: smtp.gmail.com Port: 465 or 587 Security: SSL/TLS or STARTTLS Authentication: OAuth2 User: max@dantanas.com IMAP Server: imap.gmail.com Port: 993 Security: SSL/TLS Authentication: OAuth2 What I have already done Verified DNS MX and DKIM records on the domain (email receiving works). Confirmed I can log in to the account in a browser with no issues. Tried both port 465 and 587. Removed and re-added SMTP servers in Thunderbird. Forced Thunderbird to attempt OAuth2 authentication, but the OAuth window never appears. Tested other clients, which authenticate correctly — suggesting the issue is specific to Thunderbird. Expected behavior Thunderbird should open a Google OAuth browser window to authenticate SMTP. This never occurs, which prevents SMTP from working entirely. Request Could you please advise: Why Thunderbird does not open the Google OAuth authentication window for SMTP? Whether there is a known issue affecting Google Workspace OAuth in Thunderbird? How to reset or repair Thunderbird’s OAuth behavior? Why Thunderbird does not allow the creation or use of a Junk/Spam folder for this account? Any guidance would be appreciated. I’ve spent considerable time troubleshooting, and resolving the OAuth prompt issue is essential for SMTP functionality. Thank you, Max Makowski max@dantanas.com