The simple answer is that you cannot stop spammers from using your email address in the From: or Reply to: fields.
Once a spammer (or the software they use) has discovered or guessed your Email address then it is perfectly easy for them to send spam Email forging your Email address as the sender.
Sadly it happens all the time. Thankfully, this is usually only a short-term problem and after a day or two the flow stops. Typically the fall-out is that you start receiving all sorts of failed delivery messages. You simply have to take this problem on the chin and delete the unwated messages (you can report mis-directed bounces via SpamCop if you wish but this will not stop the problem but may help).
Andrew (agsteele) [with edits since it is out of context]
It usually lasts about a week, starting with maybe 100-200 bounces received per day for the first 2 or 3 days and then tailing off towards the end. It's very annoying but if you have patience you will find it doesn't last very long.
1. You can minimize the impact if you can turn off the blanket address feature and setup specific email addresses.
2. Reporting the bounces does NOT report the spammer. It reports the server that is bouncing the forged return address. I believe it is still against the rules to report the original spam inside the bounce.
Steven P. Underwood, DNRC
Adapted From the FAQ
There are two kinds of bounces: SMTP rejects that go directly back to the server that sent the message and email bounces after accepting the message.
Email bounces are allowed by RFC (netiquette rules for the internet). Once email bounces were a very useful feature. The spammers spoiled it. Now the spam bounced with forged addresses is just a big a nuisance as the original spam.
Most mail servers do an SMTP reject, which means that any bounce message will come from the original sending mail server.
There are some mail server operators that claim that it is not practical to convert to SMTP rejects instead of bouncing.
These mail server operations must be bigger than AOL.COM which had several years ago announced on the spam-L mailing list that they recognized that such bounces where abusive to the rest of the internet
and were switching over to only using SMTP rejects.
AOL changed their policy because of the complaints they got.
Edited by dbiel, 20 June 2006 - 01:19 PM.