Installation & advice
Add an HTML signature in Thunderbird
Thunderbird accepts an HTML signature file directly. Keep that file in a stable local location.
Use your downloaded file
- Download the .htm file from InboxSig. In Thunderbird, open Account Settings and select the account.
- Enable Attach the signature from a file instead and choose your downloaded .htm file. Alternatively, enable Use HTML in the Signature text editor and paste the HTML source.
- Compose in HTML mode and send a test. Plain-text messages will not retain images or rich formatting.
Menus vary by release and account policy. Instructions reviewed 19 Oct 2026. Official documentation ↗
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