How to add an HTML or text signature in Thunderbird

A Thunderbird email signature is set in Account Settings: select your account in the left panel, then type into the Signature text field for plain text, tick Use HTML for markup, or tick Attach the signature from a file instead to load a finished file. These steps follow Mozilla’s Signatures help page for Thunderbird, read on 5 October 2026 (Mozilla shows it as last updated 8/27/25). Two more Mozilla pages, on identities and on account settings, fill in the gaps.

How to add signature in Thunderbird: the three routes

Mozilla describes two basic methods. Simple text signatures are made in Account Settings for the chosen mail account. Signatures where you want more control over positioning, or an image, are made in the Write composing window with its formatting tools and then attached from a file. The page splits the first into plain text and HTML, so there are three routes.

Route	Where you set it	What Mozilla says about it
Plain text	Signature text field	Works with messages formatted in HTML and in text
HTML in the box	Use HTML tick, then markup in Signature text	In a text-format message, text characters replace the markup
Attached file	Attach the signature from a file instead, then Choose…	File can hold plain or HTML-formatted text

Four plain lines need the first route. A logo, coloured rule and links need the third, or the second if you are comfortable with raw markup.

Add a plain text Thunderbird email signature

1. Click the menu button, or use Tools on the Menu Bar, and choose Account Settings.
2. In the left panel, select the account you want the signature for.
3. Enter the text into the Signature text field.

Mozilla’s example is three short lines: a name, a title and an organisation. It says plain text signatures work with messages formatted both in HTML and in text, so this route never breaks on the recipient’s side. Our guide to the plain text email signature has line layouts if you want a tidy one.

If you have several accounts, repeat the steps. Mozilla says you must configure signatures separately for each account.

Add a Thunderbird HTML signature with Use HTML

To use HTML formatting, Mozilla says to check Use HTML and format the Signature text with the HTML mark-up you want. If you send messages in text rather than HTML format, text characters are substituted for the markup.

That is all the page says about this box. It does not say how long the markup may be, which tags are accepted, or whether you can paste a rendered design instead of source code.

For our own product, emailfooter’s built-in Thunderbird steps use this route: copy the raw HTML, open Account Settings, tick Use HTML, paste into Signature text. Its Thunderbird tip is that pasted HTML can look like code in the settings; write a new message to see the finished result. That tip is ours, not Mozilla’s. If you are new to markup, read what makes a HTML email signature hold up before you paste anything.

Attach a Thunderbird email signature from a file

Mozilla’s file route gives more control and is the one it uses for images. In Account Settings, tick Attach the signature from a file instead and click Choose… to select the file. The file can contain plain or HTML-formatted text.

Mozilla suggests building the file in Thunderbird’s own composer:

1. Open a new HTML-formatted message: File > New > Message, or click Write on the Mail Toolbar. Make sure the formatting toolbar is showing.
2. If the toolbar is not showing, you are composing in text. Choose Options > Delivery Format > Rich Text (HTML) Only.
3. Compose and format the signature. Many formatting functions are in the Insert and Format menus.
4. Click File > Save As > File. Choose where to save it and make sure the type reads HTML files, then give it a name and click Save.
5. Close the message window and discard the message without saving.
6. Open Account Settings, select the account, tick Attach the signature from a file, click Choose and pick the file.

The page does not say what happens if you later move or rename the file, so keep it somewhere stable.

Add a logo or image to a Thunderbird email signature

For an image from your own computer, Mozilla says to create an HTML signature as above and, while composing, use Insert > Image.

You can use an image on a web server by typing its URL where you would give a file name. Here is the trade-off, in Mozilla’s words:

• If you tick Attach this image to the message, the image goes as an attachment.
• If you do not, recipients need an internet connection to see it.
• Many people block remote content for security, which stops an unattached image from showing.

If a recipient has switched off HTML, the signature is rendered as text and images are not displayed. For which apps cope with an HTML signature, see our table of email clients that support HTML signatures.

Here is an example of the kind of design that belongs in an attached HTML file rather than in the plain text box:

Example only. The firm and person are made up. A layout with a logo and icons suits the file route, not the plain Signature text field.

Replies, forwards and where a Thunderbird email signature sits

Mozilla says a signature is appended to every message you send, new and reply. In a reply it sits by default beneath the quoted text.

To move it, go to Tools > Account Settings > your account > Composition & Addressing. Change the reply style to Start my reply above the quote, then set and place my signature to below my reply (above the quote). Mozilla notes this can be set for each account and for each identity.

Mozilla’s account options page lists two switches in the same panel:

• Include signature for replies: disable it if you do not want a signature added to replies.
• Include signature for forwards: enable it to have Thunderbird add the signature when you forward.

The page does not say which is on in a fresh install, so open the panel and look.

One Thunderbird email signature for each identity

An identity is a separate configuration inside one account. Mozilla’s Using Identities page (shown as last updated 6/2/26) says the default identity holds your name, address, storage location and signature, and that you can add more.

To add one, click the Thunderbird app menu, then Account Settings, then the account in the left sidebar. Click Manage Identities… at the bottom right, then Add. The identity dialog has a Settings section (name, address, signature), Copies & Folders, and Composition & Addressing (text format, quote handling, signature). When you write a message, pick the identity from the From drop-down.

This is how you would give a shared address like sales@ its own signature. For the wider question of who gets which design, see different email signatures for different departments.

What Mozilla’s pages do not say about a Thunderbird email signature

• Size limits. No maximum signature length, file size or image dimension is stated.
• Which HTML is safe. The page does not list tags or CSS that Thunderbird accepts.
• Version differences. The pages give the menu button and Tools as two ways in. They do not map either to a Thunderbird version.
• Saving. The steps do not mention an OK or Save button after the settings change.

When your Thunderbird email signature does not appear

1. Wrong account or identity. Signatures are set per account, and per identity if you use them. Check the one in the From field.
2. Reply or forward. Look at Include signature for replies and Include signature for forwards in Composition & Addressing.
3. Text-format message. In a text message, HTML markup is replaced by text characters, so a designed signature will look plain.
4. Missing image. Remote content may be blocked, or the image was not attached to the message.
5. Moved file. If you use a file, make sure the Choose… path still points to it.

A Thunderbird email signature for a whole team

These settings live in each person’s own Thunderbird, so ten people get ten slightly different signatures unless someone shares the file. emailfooter is a free WordPress plugin where a company designs one signature and each employee follows numbered steps for their mail app, with Thunderbird among its 16. It does not write into Thunderbird for anyone, and it is English-only for now. For the general method behind all this, see how to set up an email signature. Whichever route you pick, a Thunderbird email signature is only as consistent as the file or text people actually use, so send a test message before you call it done.

Frequently asked questions

How do I add a Thunderbird email signature?

Open Account Settings, select your account and type into the Signature text field. Mozilla’s page also offers Use HTML and Attach the signature from a file instead.

Can I use a Thunderbird HTML signature?

Yes. Tick Use HTML and write the markup in Signature text, or attach an HTML file. Mozilla warns that recipients who cannot view HTML will see text, without images.

How do I attach a signature file in Thunderbird?

In Account Settings, tick Attach the signature from a file instead, click Choose… and select the file. It can be plain or HTML-formatted text.

How do I put my Thunderbird email signature above a reply?

In Composition & Addressing, set the reply style to Start my reply above the quote, then place the signature below my reply (above the quote).