Well, to delete an email message you have to select it. That means you click on it. If the Message View pane is enabled then you will see its contents. I don't know if you consider that to be "opening" it. Many users would take the view that if the Message View pane were disabled then the message doesn't get opened. I'm not so sure; if the Message View pane is hidden or shrunk, that doesn't necessarily mean that all the background code for parsing the message doesn't get run when you select the message. It's like hiding under the bedclothes so the monster under your bed can't see you. You not being able to see It doesn't necessarily mean the monster isn't really there. But we all know that hiding under the bedclothes makes us safe, yes? Close or disable the Message View if it makes you feel happier. Then you can select the message and delete it without seeing its contents. You can also right-click it and choose delete from the pop-up menu, but you have still selected it. Thunderbird will not and can not run scripts in email messages. So you can't have evil software running silently. If you choose to open an attachment, run it and become infected that's because you chose to do it. Attachments can't open themselves. The remaining risk is a webbug in an html mail message, and the default option not to allow remote content will deal with that. If you want to be ultra cautious, read your messages offline or disable html. By and large, I suspect that you are worrying unnecessarily.