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- Select View > Toolbars > Customize (to bring up the customize toolbar window)
- In the Customize Toolbar Window, Find the icon titled "Mail Views." This icon has the word "View to the left and a dropdown menu with the word "All" as the first option.
- Drag and drop the icon onto a blank space on the Thunderbird toolbar. Available space will be highlighted in white. Click "OK" to exit the Customize Toolbar window.
- Choose "Unread" from the "Mail Views" drop-down menu to automatically sort your e-mail by unread status.
- You may customize the menu by adding options such as displaying unread message from the last few days or viewing unread messages that have attachments or from a certain person.