How to set up Thunderbird

The instructions and screenshots in this setup guide are for the latest version of Thunderbird, which you can download for free for Windows, macOS, or Linux.

You can easily add your Fastmail account to Thunderbird using the setup guide in the Settings → Import & Setup screen. The general setup instructions are below.

Thunderbird needs its own app password to access your information. If you use your normal password or your Fastmail two-step verification password in Thunderbird, syncing won't work and you will see a password error.

Set up your email

  1. Open Thunderbird. The Set Up an Existing Email Account dialog box will appear. If it doesn't, select Local Folders in the sidebar on the left, then under the Set up an account heading in the page that appears, click the Email link.

    Set Up a new email on Thunderbird

  2. Fill in your name, email address, and app password:

    • Your name: Whatever name you want others to see on the email you send.
    • Email address: Your full Fastmail username, including the domain.
    • Password: Your Thunderbird app password. (What is an app password?)

    Click Continue. Thunderbird will find the server settings.

    Set Up an Existing Email Account

  3. Click Done. Thunderbird will fetch the list of your folders and start synchronizing your mail. If this doesn't seem to be happening, close and reopen Thunderbird; it sometimes gets stuck the very first time it tries to connect.

    Autodetected settings of Fastmail

Adding your other email addresses

To use a different email address to your Fastmail username:

  1. Open Thunderbird. Click your account name in the sidebar (just above the Inbox).
  2. Click View settings for this account.
  3. Click Manage Identities…, then click Add…
  4. Fill in Your Name and Email Address with the name and email you want your messages to come from.
  5. Click OK to save the new identity. If you want it to be the default, click Set Default then close the identities panel. Click OK to close the account settings dialog.

You will now be able to choose the address you added to send messages from when you compose new messages in Thunderbird.

Set up your calendar

To add calendar support to Thunderbird, you need to install the Lightning extension. Once you have installed this, follow the instructions below to sync your calendars with your Fastmail account. Lightning does not support autodiscovery of calendars, so you will need to repeat these steps for every calendar you wish to synchronize with Fastmail.

  1. Open Thunderbird. The Set Up an Existing Email Account dialog box will appear. If it doesn't, select Local Folders in the sidebar on the left, then under the Accounts section click the Create a new calendar link.

    Create a new calendar

  2. Select the option to store your calendar On the Network, then click Next.

    Calendar on Network

  3. Lightning does not support calendar autodiscovery, so you now need to get the address of the calendar you wish to synchronize. To do this, log into your Fastmail account and go to the Settings → Calendars screen. Find the calendar you wish to add to Lightning and click the Export link. A popover will appear with the CalDAV address already selected. Press Ctrl+C, or Right-click and click copy to copy the address.

    Fastmail Web calendar address

  4. Paste this address into the Location input, and select CalDAV as the Format above. If you want to be able to access your calendar offline, tick the Offline Support option. Click Next.

    Pasted web calendar address in location field

  5. Give your calendar a name and pick a color. To avoid confusion, you probably want to give it the same name and a similar color to that used in the web interface or other CalDAV clients. Click Next.

    Calendar name and Color picker

  6. After a moment, you will be prompted to authenticate. Fill in your username and app password:
    • User Name: Your full Fastmail username, including the domain.
    • Password: Your Thunderbird app password. (What is an app password?). Tick the option to Use Password Manager to remember this password. Click OK.

      Authentication using Username and Password

  7. Click Finish.

Your calendar has now been added to Lightning and should synchronize with Fastmail. Repeat these steps to add any other calendars in your Fastmail account.

Set up your contacts

Thunderbird does not natively support CardDAV synchronisation. You will need to install a third party adapter to use CardDAV, such as CardBook.

Be aware that any pre-existing contacts already on your device do not automatically get copied back up to Fastmail with the sync: you need to import them to Fastmail first.


  1. Install the Thunderbird Add-On CardBook through Thunderbird's add-on manager.
  2. Click on CardBook in the Thunderbird menu bar.
  3. Click the menu button Menu button on the top left, hover over Address Book, and choose New Address Book.
  4. On the Add a new address book dialog box, choose Remote and click Next.
  5. Choose CardDAV and enter the following details:
    • URL:
    • Username: Your Fastmail email address
    • Password: Create a new app password with CardDAV access in the Fastmail web interface. Use this app password for CardBook.
  6. Click Validate and if the settings entered are correct, the greyed out Next button will become active and you can click on it.
  7. If you are a member of a multi-user account, you will have shared contacts as well as personal contacts. You can choose to sync one or both. Choose your contact list color and leave the vCard setting as 3.0.
  8. Click Next and Finish.
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