Only email servers can bounce messages as non-deliverable. Once you have a message it has been delivered. The worst thing you could do is reply to this type of message since you are confirming it arrived at a working address. Just delete them.

OK. I know it isn't a real real bounce but a reply e-mail which looks just like a bounce message. (Maybe it's 'sender' address is also changed and disguised as a mail server.)

When I still used Incredimail and I 'bounced' a spam or fishing e-mail, usually they stopped sending other emails.

Now that I use Thinderbird and cannot send a 'bounce' e-mail, the scum of the earth don't get a 'bounced e-mail return message, which confirms them that my e-mail address is in use. Now I get loads and loads of fishing e-mails. It just won't stop.

As long as the scammer don't look to closely to the bounce-message they get, this pseudo-bouncing really seems to fool them.

So how can I 'bounce' messages in Thunterbird?

Why hasn't Thinderbird this simple function? I will have to start using that Incredimail again, which I really don,t like.

Thunderbird does not have this function because replying to spam is the dumbest thing you could do.

Well, Thunderbird should have this function, because, believe it or not, most of the time it really fools the spam/fishing e-mail sender in believing your e-mail address does not exist and it will be removed from there mailing list.

Even, as you say, you do not reply to an spam/fishing e-mail, not getting a bounced message, confirmes your e-mail address is valid and then the bombardment of spam/fishing really begins.

So don't say it is a stupid function, because since I stopped using Incredimail and started using Thunderbird, I have never ever seen so much repetitive spam/fishing e-mails in my inboxes. It just won't stop.

Spammers and phishers rarely send out their material using their own computers. The from: address is usually one harvested from web forums, newsgroups and the like. In the vast majority of cases your "bounce" would go to the unfortunates whose email addresses have been misappropriated.

Spammers don't use their own computers, or their own email accounts to send out their stuff. They use botnets, networks of "owned" computers. And most of the time they don't care about replies via email. They want you to visit websites and become "owned" yourself, or to pay money for some non-existent product or service.

I'm really surprised that you think you have found that bouncing is productive.