Their internet address is as I would expect.
firstname.lastname.@domainame.com
Here's the header from an email address for an account I created
From John Doe Fri Mar 6 00:53:15 2009
Return-Path: <john.doe@domainname.com>
Authentication-Results: mta148.mail.re3.yahoo.com from=srvrhlscalix.domainname.com; domainkeys=neutral (no sig); from=srvrhlscalix.domainname.com; dkim=neutral (no sig)
Received: from xx.xxx.xxx.xx (EHLO srvrhlscalix.domainname.com) (xx.xxx.xxx.xx)
by mta148.mail.re3.yahoo.com with SMTP; Thu, 05 Mar 2009 16:53:16 -0800
Received: from srvrhlscalix.domainname.com (localhost [127.0.0.1])
by srvrhlscalix.domainname.com (8.12.11.20060308/8.12.11) with ESMTP id n260rFPv018564
for <myaddress@yahoo.com>; Thu, 5 Mar 2009 19:53:16 -0500
Date: Thu, 5 Mar 2009 19:53:15 -0500
From: John Doe <Doe@srvrhlscalix.domainname.com>
To: myaddress <myaddress@yahoo.com>
Message-ID: <H00001150101a95c.1236300795.srvrhlscalix.domainname.com@MHS>
Subject: test5
x-scalix-Hops: 1
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="2_0_112_5ed2a41MHTML_=_01"
Content-Length: 554
the return path is correct but the from is incorrect. However this is just with new accounts we create and only from outlook.