If Thunderbird is specified as your system's default email application, it will integrate with other applications (such as word processors and web browsers). For example, when you click an email address link (like "This email address is being protected from spambots. You need JavaScript enabled to view it.") on a web page or invoke a mail function (such as "Send to") from a word processor, Thunderbird will launch and open a message composition window.

Force Thunderbird to check if it is the default

Thunderbird can be configured to check if it is the operating system's default mail client each time it is started.

1. At the top of the Thunderbird window, click the Tools menu and select Options, or click the menu button  and choose Options.
2. On the Advanced panel, select the General tab.
3. Make sure that "Always check to see if Thunderbird is the default mail client on startup" is checked.
4. Click Check Now to check if Thunderbird is set as the default mail client immediately.

• If you want to set Thunderbird as the default client for e-mail, newsgroups or feeds, check the corresponding boxes and click OK. When a box is grayed out, Thunderbird is already set as the default client for that purpose.
• If you set Thunderbird to be the default mail client, other applications (such as your web browser or word processing application) may need to be restarted for the changes to take effect.

Set Thunderbird as the operating system default

Set Thunderbird as an application default

In some cases (such as Firefox on KDE Linux), the application doesn't check the operating system preferences to determine the default email application. When that is the case, you must set the default in the application itself. Refer to the application documentation for instructions.