In response to the SMTP authentication loops or invalid_scope errors encountered when using Thunderbird on Ubuntu, here is a solution based on practical experience.

1. Core Steps: Bypassing SMTP Lockouts via Owl

When the traditional SMTP path is completely blocked, you must switch to the web authorization path via the Owl for Exchange plugin.

• Plugin Acquisition: Visit

https://www.beonex.com/owl/#fh5co -work.

Menu Entry: Click the "Folded Menu" in Thunderbird.

Functional Path: Select "Add-ons and Themes."

Manual Operation: Go to "Owl for Exchange", click "Preferences", and then select "Add new account manually ......"

Key Parameters: Set Protocol to Outlook Web Access and Webmail page to https://outlook.office.com/owa/.

Privacy: Enable "Encrypted Subject" in Thunderbird's native OpenPGP settings to prevent title leakage.

2. Privacy Hardening: Solving Email Subject Leakage

To address the flaw where plugins like Mailvelope cannot encrypt email titles, it is recommended to return to Thunderbird's Native OpenPGP.

• Key Association: Associate your existing PGP key in the "End-to-End Encryption" section of Account Settings.
• Subject Protection: Check the "Encrypted Subject" option.
• Encryption Effect: The original title will be securely wrapped within the encryption block, with only a placeholder displayed externally to ensure communication intent is not monitored.

By following this plan, developers can resolve SMTP authentication obstacles while simultaneously building a robust privacy moat.