My setup is possibly a bit unusual, so let me give you some background.

The way I deal with spam, is I have a (sub)domain with a catchall address. Every site/service I have to sign up for, I put down a different email address. It all ends up in the Catchall box anyway. This way I can monitor who sends me what, and which companies are abit too flexible with their(or my) privacy concerns. As soon as one of the addresses gets spam, I block that specific 'to' address, and no more spam.
I used to create an alias for every site/service, but decided this is too much work, hence the catchall address.

Now, I used to host my mail on a cPanel controlled server, which has the ability to create a 'forwarder' that rejects messages based on the 'to'-address. Is this possible with Zimbra? And how?

I found a lot on blocking senders, but that doesn't really work well for me. I want to make the address they're sending to disappear.