Your calendar has now been added to Lightning and should synchronize with Fastmail. Tick the option to Use Password Manager to remember this password. Password: Your Thunderbird app password.User Name: Your full Fastmail username, including the domain.After a moment, you will be prompted to authenticate.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. Give your calendar a name and pick a color.If you want to be able to access your calendar offline, tick the Offline Support option. Paste this address into the Location input, and select CalDAV as the Format above.
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Press Ctrl+ C, or Right-click and click copy to copy the address. A popover will appear with the CalDAV address already selected. Find the calendar you wish to add to Lightning and click the Export link. To do this, log into your Fastmail account and go to the Settings → Calendars screen. Lightning does not support calendar autodiscovery, so you now need to get the address of the calendar you wish to synchronize.Select the option to store your calendar On the Network, then click Next.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. The Set Up an Existing Email Account dialog box will appear. Lightning does not support autodiscovery of calendars, so you will need to repeat these steps for every calendar you wish to synchronize with Fastmail. Once you have installed this, follow the instructions below to sync your calendars with your Fastmail account. To add calendar support to Thunderbird, you need to install the Lightning extension.
![thunderbird for mac latest version thunderbird for mac latest version](https://i0.wp.com/www.macsoftdownload.com/wp-content/uploads/2017/08/Thunderbird-mac.jpg)
You will now be able to choose the address you added to send messages from when you compose new messages in Thunderbird. Click OK to close the account settings dialog. If you want it to be the default, click Set Default then close the identities panel.
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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. Thunderbird needs its own app password to access your information.
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The general setup instructions are below. You can easily add your Fastmail account to Thunderbird using the setup guide in the Settings → Import & Setup screen. 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.