sendmail: Routing dead mail to a shell command?
 

Is there a way that I can run a shell command when an email is returned from a server because the account doesn't exist? People sign up on my site using fake email addresses sometimes and then I get a bunch of dead mail bouncing back to me. I'd like to be able to run a shell command that would call up a script to remove their email address from the database any time an account comes back dead. Thanks.

In /etc/aliases you can add a line like:
xyz :|/path/to/script

This will send all mail sent to user "xyz" to that program/script. You may want to consider using a scoreboard and only delete mail once it has been rejected say 3 times in a row - this should account for any network issues.

After editing /etc/aliases you need to run:
newaliases