How to remove the signature separator in Thunderbird

Why remove the signature separator?

When you set up a signature in Thunderbird, a -- delimiter (two dashes followed by a space) automatically appears above it. This separator is a convention inherited from the email standards (RFC 3676), but it is not always wanted, in particular in order to:

• Keep a clean, professional layout for your emails
• Avoid visual redundancy if your signature already contains a separator
• Tailor the appearance of your messages to your own preferences
• Improve readability in certain email clients

Side effect to know: the -- delimiter also lets email clients recognise the signature and omit it from quoted replies. Removing it improves the look of your messages, but your signature may then reappear in conversation threads.

The problem in detail

By default, Thunderbird automatically inserts a separator made up of two dashes followed by a space (-- ) before your signature. Here is an example of what you see:

Your message content

-- 
Your signature
Firstname Lastname
Email: contact@example.com

This behaviour is standard in most email clients, but it can be turned off if you prefer a different result.

Step-by-step solution

To remove the signature separator in Thunderbird, follow these steps:

Step 1: Open Thunderbird

Launch the Thunderbird application on your operating system.

Step 2: Go to the settings

1. Click the hamburger menu ≡ at the top right of the window
2. Select Settings (or Paramètres in French)
3. In the left-hand panel, choose General (or Paramètres généraux)

Step 3: Open the Config Editor

1. Scroll to the bottom of the General settings page
2. Click the Config Editor... button
3. Accept the warning that appears: “Caution! Changing advanced settings can affect the performance and the security of this application.”

Step 4: Change the preference

In the Config Editor search bar, type:

mail.identity.default.suppress_signature_separator

1. Double-click the matching line to change its value
2. Change the value from false to true
   • Important note: the suppress_signature_separator preference means “suppress the separator”. So true = remove (do not display) and false = display (the default behaviour)
3. The value should now appear in bold to indicate that it has been modified

Step 5: Check the result

Close the Config Editor and the settings. Create a new message to check that the separator has indeed gone.

Expected result

Once changed, your signatures appear directly, without the dashes:

Your message content

Your signature
Firstname Lastname
Email: contact@example.com

Per-identity configuration

If you use several identities in Thunderbird (several email accounts), set the option for each identity:

1. Open the Config Editor as described above
2. Search for suppress_signature_separator
3. Set every listed mail.identity.idN.suppress_signature_separator entry to true (in addition to mail.identity.default.suppress_signature_separator if needed)

You do not need to look up an identity number in an address bar: the Config Editor already lists every matching preference.

Troubleshooting

The preference does not appear

If you cannot find mail.identity.default.suppress_signature_separator, create it manually:

1. In the Config Editor, click the + button or right-click
2. Select New > Boolean
3. Enter the name: mail.identity.default.suppress_signature_separator
4. Set the value to true

The separator comes back after an update

Check that the preference is still set to true in the Config Editor. Major updates can sometimes reset certain preferences.

The change does not take effect immediately

Sometimes you need to:

• Close Thunderbird completely and reopen it
• Create a new message (messages that are already open may keep the old format)

Compatibility

This solution works on:

• Thunderbird 115 and later, including current ESR builds (128 / 140)
• All operating systems: Windows, macOS, Linux

Note on about:config

The Config Editor opened from Settings → General is Thunderbird’s about:config interface. That is the reliable path. Avoid the quick search bar (Ctrl+K / Cmd+K): it does not always open this interface.

Additional resources

• Removing the signature separator (MozillaZine)
• RFC 3676 — signature delimiter
• Thunderbird community forum

This change lets you tailor the appearance of your emails to your own preferences, while keeping every other Thunderbird feature intact.