LLM-powered pre-send email checks for Thunderbird.
Outbound Guardian intercepts the Send action in Thunderbird to run your custom checks through an LLM. If any check triggers, the send is blocked and a warning dialog lets you edit, auto-fix, or send anyway.
- Define check rules in plain language (e.g. "contains em-dash characters" or "tone is too informal")
- Click Send — each rule is evaluated by the LLM against your email
- If any rule triggers, a warning dialog appears with options:
- Edit — return to the compose window to fix manually
- Auto-fix — the LLM rewrites the email based on your improvement instructions
- Send anyway — override the warning
- Thunderbird 128 or later
- An OpenAI API key
Search for "Outbound Guardian" in Tools → Add-ons and Themes, or visit the ATN listing.
- Clone this repo
- Open Thunderbird → Tools → Add-ons and Themes
- Click the gear icon → Install Add-on from File...
- Select
manifest.jsonfrom the project root
- Go to Add-ons → Outbound Guardian → Options
- Enter your OpenAI API key
- Click Test Connection to verify
- Click Save Settings
- Click Add Rule to create your first check
| Rule Name | Condition | Improvement |
|---|---|---|
| Em-dash check | contains em-dash characters (—) | Replace em-dashes with standard dashes or commas |
| Tone check | tone is too casual or informal for a business email | Adjust tone to be professional while keeping the same meaning |
| Repetition | contains repetitive phrasing or redundant sentences | Remove repetition and make the writing more concise |
Your email content is sent to the OpenAI API using your own API key. No data is sent to the extension developer or any other third party. See the privacy policy for details.
MIT