That's relatively easy. I use the following:
Thanks! My recipe for sendmail is here (section Sendmail workaround, near the end of the page), copied from a post on the sendmail newsgroup.
<http://mozilla.wikia.com/wiki/User:Me_at_work/plushaters>Every time I look into Postfix it looks so much simpler, and your example, even with the complicated regex, confirms that.