From MozillaZine Knowledge Base

Usually if you go to "Tools -> Account Settings -> Server Settings" and check the box that says "Check for new messages at startup" Thunderbird will start in the Inbox folder. If you have more than one account, Thunderbird will start in the Inbox of your default account, which is the account displayed at the top of the folders pane. To make another account into your default account, go to "Tools -> Account Settings", select the account you want to make the default, and click the "Set as Default" button.

However, that doesn't always work in recent versions. There are a couple of add-ons you can use as workarounds.

• The Select Inbox add-on specifies the startup folder.
• The Folderpane Tools add-on lets you customize the folder pane. Accounts can be rearranged and the startup folder chosen.
• The Manually sort folders add-on is mainly used to sort the order of folders in the folder pane. However it also lets you specify the startup folder.

Opening some other folder

You can also specify any folder as the startup folder (doesn't have to be an inbox) by changing the command used to start Thunderbird. For example, the command might be in the properties of an icon on your desktop. At the end of the command, add -mail followed by the URI of the folder that you want to open.

For example, here is a command that starts Thunderbird on Windows, opening a Templates folder:

"C:\Program Files\Mozilla Thunderbird\thunderbird.exe" -mail mailbox://someone@pop.example.net/Templates

You can use this method to make a collection of icons that directly open various folders.

See also

• Turn off or change the Start Page