The Unwanted Mail Client
When you are browsing the web on Ubuntu Linux and click a “Contact Us” link (technically known as a mailto: link), the operating system intercepts that click. Instead of simply opening a webmail portal like Gmail in a new browser tab, Ubuntu will automatically launch its default desktop email client—usually Mozilla Thunderbird or GNOME Mail. If you have never set up Thunderbird and exclusively use web-based email, this automatic launch is incredibly jarring. You are suddenly presented with a complex setup wizard demanding server addresses and passwords, completely interrupting your web browsing workflow.
Redirecting the Mailto Protocol
To streamline your communication workflow and stop Ubuntu from automatically opening a desktop application when you click e-mail links, you must change the default system handler for the mail protocol.
Click the system menu in the top-right corner of your screen and open Settings. In the left-hand navigation sidebar, scroll down and click on Default Applications. Look for the entry labeled Mail. By default, this will show Thunderbird. Click the dropdown menu. If you want links to open in your browser (assuming your browser is configured to handle mail links), select your web browser (e.g., Google Chrome or Firefox). If you simply want nothing to happen when you accidentally click an email link, there isn’t a “None” option in the GUI. In that case, open your terminal and type xdg-mime default org.gnome.Nautilus.desktop x-scheme-handler/mailto to purposefully break the handler, preventing any mail app from launching.