Situation: On a Unix with sendmail, I always made it a practice to put a '.forward' in roots home directory that emailed my Outlook account with any root messages but *also* kept a backup copy of the message in roots mailbox using the syntax of '\root' in the .forward file. This is a well defined behavior in .forward files to prevent endless alias expansion. After upgrading the machine to zmailer, the first time an email went to root, it started a chain-reaction endless looping error message in roots mailbox about an invalid .forward file (it doesn't like the '\' character).
Either error channel needs to recognize these looping situations and stop itself after a few times or the code that handles .forward file should start recognizing the '\' syntax. Seems like normal users could use exploit this flaw to do a local Denial of Service attack on /var disk space.