If you want to delete a message, you have to highlight it — click on it — first. There's no way around that, but you can disable the pane that opens messages as soon as you do that. Without that message pane, it's fast and easy to delete emails sans opening them.
Delete a Message Without Opening it First in Mozilla Thunderbird
To remove an email in Mozilla Thunderbird without opening it:
- Click on the message with the right mouse button (or hold down Ctrl while clicking on a Mac).
- Select Delete Message from the menu.
To delete multiple messages in one go, you can hide the preview pane:
- Select View | Layout | Message Pane from the menu so that the item is not checked.
- Highlight the desired message or messages in the message list.
- Press Del.
Of course, you can enable the message pane again using the same menu command as above.