Why is my Thunderbird signature showing as plain text?

You need to check the 'Use HTML' checkbox in Account Settings. Without it, HTML is treated as plain text and the code is shown instead of the formatted result.

Does Thunderbird support images in email signatures?

Yes. Images hosted at a public URL (like DropSig-hosted images) work in Thunderbird. Recipients need to allow remote images to see them.

Can I use Thunderbird with a Gmail or Outlook account?

Yes. Thunderbird works with Gmail, Outlook, Yahoo, and any IMAP/POP3 email account. The signature settings are the same regardless of which email service you use.

How do I add a signature to replies only in Thunderbird?

By default, Thunderbird appends your signature to all emails including replies. To disable it for replies, go to Account Settings and uncheck 'Automatically add my signature' or adjust the signature placement setting.

How to Add an HTML Email Signature in Mozilla Thunderbird

Thunderbird is a free, open-source email client that supports HTML signatures. There's one required step that many people miss: you need to check 'Use HTML' in the Account Settings, or your signature will appear as plain text. Here's the full process.

Before you start

You'll need a signature to paste. Already have one? Skip to step 1.

Create your signature first →

Step-by-step setup

In Thunderbird, right-click on your email account in the left sidebar and select "Settings". Or go to the menu (☰) → Account Settings.

In the Account Settings window, click on your email account in the left sidebar (not a subfolder, but the main account entry).

You'll see a "Signature text" section in the main panel. Below the text area, you'll see a checkbox that says "Use HTML".

Check the 'Use HTML' checkbox. This is required for your signature to render as formatted HTML instead of plain text.

Pro tip: Without this checkbox, any HTML you paste will appear as raw code in the signature.

In DropSig, right-click "Copy Signature" and look for "Copy as HTML" if available, or use the standard Copy Signature button.

Click inside the signature text area in Account Settings and paste (Ctrl+V). The signature will appear as formatted HTML.

Click "OK" to save Account Settings. Compose a new email to verify the signature appears correctly.

Common issues

Signature shows as raw HTML code

You haven't checked the 'Use HTML' checkbox in Account Settings. Go back to Account Settings, check that box, then re-paste your signature.

Images not showing in the signature

Thunderbird may block remote images by default. In a compose window, look for the 'Remote content blocked' bar and click to allow. Alternatively, use 'View → Message Body As → Original HTML' to troubleshoot.

Signature only appears for one account

Each account in Thunderbird has its own separate Account Settings and signature. If you have multiple accounts, configure the signature in each one separately.

FAQ

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Last verified: March 2026