How to Do a Thunderbird Mail Merge: Send Personalised Emails (2026)

Want to send personalised emails to a list of people, with each message addressed by name, without typing them one by one? Thunderbird mail merge does exactly that. With the free Mail Merge add-on for Mozilla Thunderbird, you write one template, pull names and other details from a spreadsheet, and Thunderbird creates and sends an individual email to each recipient. Here’s how to do a Thunderbird mail merge in 2026, step by step.

Quick answer: Install the Mail Merge add-on, write a message with placeholders like {{FirstName}}, put your recipients in a CSV file with matching column headings, then click Mail Merge in the compose window, choose the CSV file and send (or save as drafts to check first).

Why use Thunderbird mail merge?

If you put everyone in the To or BCC field, every person gets exactly the same message. Mail merge creates a separate email for each person, so you can add their name, company, invoice number or any other detail. Each recipient sees only their own address, which also protects everyone’s privacy. It’s ideal for event invitations, club newsletters, client updates, job applications and small business announcements.

Step 1: Install the Mail Merge add-on

1. Open Mozilla Thunderbird and go to Tools → Add-ons and Themes (or the ≡ menu).
2. Search for Mail Merge by Alexander Bergmann and click Add to Thunderbird.
3. Restart Thunderbird if asked.

The add-on is free and regularly updated. Version 11.5 (March 2026) supports Thunderbird 140 ESR and the latest monthly releases.

Step 2: Create your recipient list (CSV)

In Excel, Google Sheets or LibreOffice Calc, put your column names in the first row, such as Email, FirstName and Company, with one recipient per row below. Save or download it as a CSV (UTF-8) file.

You can also use a Thunderbird address book or a JSON file as the data source.

Step 3: Write your template

1. Click Write to open a new message.
2. In the To field, type {{Email}} (matching your email column name).
3. Write the subject and body, and insert placeholders in double curly braces wherever you want personal details, for example: Hi {{FirstName}}, thanks for working with {{Company}}...
4. Placeholder names must match the CSV headings exactly, including capitals and spaces. Add attachments if needed.

Step 4: Run the mail merge

1. In the compose window, click the Mail Merge button (or find it in the File menu).
2. Choose CSV as the source and select your file, checking the character set and field separator (comma or semicolon).
3. Pick a Delivery Mode: Save As Draft to review messages first, Send Later to put them in the Outbox, or Send Now.
4. Optionally set a pause between messages, then click OK.

If you chose Send Later, use File → Send Unsent Messages to send everything in the Outbox. Always test with a small list that includes your own address first.

Tips to avoid problems

• Respect sending limits: Gmail, Outlook.com and most hosts limit how many emails you can send per day. Use the pause option, and use a proper email marketing service for large lists.
• Only email people who expect it to avoid spam complaints, and include a way to opt out for newsletters.
• Check placeholders: a typo leaves {{FirstName}} visible in the email. Save as drafts and check a few before sending.
• Prefer Gmail? Its Mail merge feature in some Google Workspace plans, or Yet Another Mail Merge for Google Sheets, are alternatives.

Frequently asked questions

Is Thunderbird mail merge free?

Yes. Thunderbird and the Mail Merge add-on are both free.

Can I schedule a mail merge for later?

Choose Send Later or Save As Draft, then send when you’re ready. See more ways to schedule emails to send in the future.

Does Thunderbird mail merge work with Gmail accounts?

Yes. It sends through whichever account you write from in Thunderbird, including Gmail and Outlook, subject to their daily sending limits.

Originally written by guest blogger Paul Adrian Gonzalez, a senior author and editor who uses Thunderbird to manage his busy inbox. Updated for 2026 by the QuickOnlineTips team.