The instructions and screenshots in this setup guide are for the latest version of Thunderbird, which you can download for free for Windows, Mac OS X or Linux.
Click the Skip this and use my existing email button, at the bottom of the window.
Fill in your name, email address and password:
Click Continue. Thunderbird will find the server settings.
Click the Manual config button. In the Incoming row, change the port to
Click Done. Thunderbird will fetch the list of your folders and start synchronising 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.
To use a different email address to your FastMail username:
You will now be able to choose the address you added to send messages from when you compose new messages in Thunderbird.
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 synchronise with FastMail.
Open Thunderbird. The Welcome to Thunderbird dialog 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.
Select the option to store your calendar On the Network, then click Next.
Lightning does not support calendar autodiscovery, so you now need to get the address of the calendar you wish to synchronise. To do this, log into your FastMail account and go to the Settings → Calendar screen. Find the calendar you wish to add to Lightning and click the CalDAV URL link. A popover will appear with the CalDAV address already selected. Press Ctrl+C, or select Edit → Copy from the menu bar to copy the address.
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.
Give your calendar a name and pick a colour. To avoid confusion, you probably want to give it the same name and a similar colour to that used in the web interface or other CalDAV clients. Click Next.
After a moment, you will be prompted to authenticate. Fill in your username and password:
Tick the option to Use Password Manager to remember this password. Click OK.
Your calendar has now been added to Lightning and should synchronise with FastMail. Repeat these steps to add any other calendars in your FastMail account.