Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!adm!rick@seismo.CSS.GOV
From: rick@seismo.CSS.GOV (Rick Adams)
Newsgroups: comp.mail.headers
Subject: re: ! and @ -- which RFC ?
Message-ID: <12798@brl-adm.ARPA>
Date: 4 Apr 88 17:58:50 GMT
Sender: news@brl-adm.ARPA
Lines: 7

The defacto standard is that RFC822 rules. That means that the
@ get precedence because the ! is in the "local part". Nothing
should look at the local part other than the host to the
right of the @.

You want to avoid mixing ! and @ if at all possible (and it is
almost always possible)