Where would you bounce a spam message to? Most likely, the "From:" address would be spoofed, so you'd be returning this message to the owner of the stolen email address. This person doesn't care about whether or not you're at home, and your returns to him would look to him like more spam. You're adding to the overall problem. Have you never received those "failed delivery" notifications that puzzlingly refer to messages allegedly from you that you know you never sent? Bouncing as you describe it is properly a function of the server. See if you can do this at your email provider's webmail site. The email standards don't allow for "bouncing" from an email client, which is why Thunderbird doesn't support it. There is a ''Mail Redirect'' add-on for Thunderbird, which refers to what it does as "bouncing", but it's meant to be used, typically, to pass a message that arrives in your Inbox on to someone else, usually a colleague who is better placed to deal with it. Whilst the message arrives in your colleague's Inbox with the appearance of having gone directly to your colleague from the sender, without your intervention, inspection of the message's headers will reveal the truth. So even if it sounds as if it may be useful, this add-on still offers an opportunity to a canny spammer to confirm you are using the email account in question.