You can print your emails from a browser by clicking Actions next to the header of the message, and then clicking Print.
If you are viewing a single message within a conversation thread, only the message you are viewing will be printed. If you would like to print an entire conversation thread, you will need to expand the conversation and use your browser's print function.
Printing through browser
You can print a message through your browser using the keyboard shortcut Ctrl + P (for Windows) or Command + P (for Mac).
When printing from a browser, the browser will print all expanded messages in the conversation. To expand a message in the web interface, you will need to click on the unexpanded message in the conversation. Alternatively, you can expand all messages in a conversation with the keyboard shortcut Shift + e.
Printing through Fastmail app
You can print from the Fastmail mobile app by clicking into a message, pressing the three vertical dots near the header, and then clicking Print. When printing from the app, you can only print one message at a time.