I am trying to change the configuration of exim so that it neither generates backscatter or is subject to spam floods. Currently, the configuration options are to either accept all mail to a domain using a catch-all box, subjecting you to a flood of spam in that box if there's a dictionary attack, and a lot of spam on a normal day anyway, or to accept all messages and then bounce messages to non-existent recipients, usually going to a forged sender. I do not consider "accept and discard" to be an option, as it hides when someone sends a message to a valid recipient with a typo. What I want is for exim to reject all messages to non-existent users, at the time the mail envelope is sent. I do not want to use a catch-all address. Is there a way to get exim to do this? Or alternatively, is there a way to replace exim with postfix? Also on the subject of backscatter, is there a way to globally disable Boxtrapper?