Fairsig

How to add an email signature in Thunderbird

Thunderbird doesn't have a rich signature editor. Instead, it lets you enter the signature's HTML directly or point to an HTML file. Both work well with a signature made in the Fairsig generator; the first is quicker, the second is easier to update.

Option 1: paste the HTML into Account Settings

  1. In the Fairsig generator, click Copy HTML (not Copy signature).
  2. In Thunderbird, click the menu button (≡) and choose Account Settings. With the menu bar, use Tools > Account Settings (Edit > Account Settings on Linux).
  3. In the left panel, select the account the signature is for.
  4. Check Use HTML below the Signature text box.
  5. Click in the Signature text box and paste the HTML with Ctrl+V (Cmd+V on a Mac).
  6. Write a new message from that account to check the result.

Copy HTML, not Copy signature. Thunderbird's Signature box is a text field: with Use HTML checked, it reads what you paste as HTML code. Pasting the formatted signature there would lose its layout.

Option 2: attach the signature from a file

  1. In the Fairsig generator, click Download .html and keep the file somewhere permanent (not in Downloads, if you clean it out).
  2. In Thunderbird, open Account Settings and select the account.
  3. Check Attach the signature from a file instead.
  4. Click Choose… and select the .html file.

Mozilla's help says the file can contain plain or HTML-formatted text. To update the signature later, download a new file from Fairsig and replace the old one at the same path. Keep the file in place: the setting points to that file.

Signature above or below the quoted text

By default, when you reply, Thunderbird puts your signature at the end, beneath the quoted message. To put it right under your reply instead, open Account Settings, select the account, then Composition & Addressing. Set the reply style to Start my reply above the quote, then set and place my signature to below my reply (above the quote).

HTML or plain text messages

An HTML signature only looks right in messages composed in HTML. If you write in plain text, Thunderbird substitutes text for the markup. Recipients whose mail app shows only plain text will see the text version, without images. That's another reason to keep your name, phone and email as real text, never only inside an image.

Images

  • Fairsig's signatures reference images (logo, photo, social icons) by public https address, so nothing is attached to your email.
  • Thunderbird can also insert local images when you build a signature file in its own composer (Insert > Image), with an option to attach the image to each message. Linking is lighter.
  • Recommended dimensions are on the signature size page.

Questions

Why does my Thunderbird signature show HTML code?

Either “Use HTML” isn't checked, or you're writing the message as plain text. Mozilla's help says that when you send messages in text format, text characters are substituted for the HTML markup. Check Use HTML in Account Settings, and compose in HTML (rich text) format.

Can I paste the formatted signature instead of the code?

Not into the Signature box in Account Settings: it's a plain text field, which is why Thunderbird has the Use HTML option. Paste the HTML source (Copy HTML in Fairsig), or attach an .html file.

Do I need a signature for each account?

Yes. Mozilla's help says that with several email accounts you must configure signatures separately for each one. Signature placement can also be set per account and per identity.

Will recipients see my images?

Only if their mail app shows HTML and loads remote images. Fairsig links images from public https addresses. Mozilla notes that many people block remote content, so keep your contact details in text.

Sources

Mozilla Support, Signatures (Thunderbird). The live page blocks automated access, so in October 2026 we checked its text through a public archive copy (marked “last updated 5/24/22”). If a label differs in your version of Thunderbird, look for the same words in Account Settings.

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