manually bounce back spam
In Incredimail there is an option to return spam to the sender(s) with a statement such as "Undeliverable Error code #23456789" Contact System IT with 56789 Replacement" or something else you can change ...does Thunderbird have anything like this??
Opaite Mbohovái (1)
No and it would be a bad idea. It is not bounced. It was delivered to your address and will show in the return email that the spammer found a good, active email address. And this is if the spammer actually uses their own email address which they rarely do. Most likely you would just send it back to the poor soul that had their address stolen and used to send spam. Just delete the mail and get on with it.
Moambuepyre