sender verification problem

[Antonino Balsamo]

Hi

I manage several domains (postfix configured via ispconfig, but this has 
really nothing to do with the problem) and faced this issue while 
fighting spam.

Example: I have a domain with 2 email addresses a...@example.com, 
b...@example.com. I know the legitimate sender addresses for this domain by 
reading from tables.

I receive spam from nonexist...@example.com. How do I turn on sender 
verification address only for the domain I handle and block ONLY for 
nonexistant local addresses?

thanks

Ant