Yahoo Marks It As Spam... Why?

If I'm not mistaken we have reverse DNS setup and no blacklist entries. Is there any reason why welcome emails from our custom CP are being filtered directly into the Yahoo SPAM box?

Here's the full headers from my personal email. This is the exact message a client would be sent.

From HostVentrilo.com Sun Apr 20 20:38:17 2008
Return-Path: <nobody@web.teamspeakhost.com>
Authentication-Results: mta105.rog.mail.scd.yahoo.com from=hostventrilo.com; domainkeys=neutral (no sig)
Received: from 69.93.229.114 (EHLO web.teamspeakhost.com) (69.93.229.114)
by mta105.rog.mail.scd.yahoo.com with SMTP; Sun, 20 Apr 2008 20:38:18 -0700
Received: from nobody by web.teamspeakhost.com with local (Exim 4.68)
(envelope-from <nobody@web.teamspeakhost.com>)
id 1JnmrB-0007AT-P3
for xxxxx@rogers.com; Sun, 20 Apr 2008 23:38:17 -0400
Received: from phpmailer ([67.204.23.77])
by www.hostventrilo.com with HTTP (PHPMailer);
Sun, 20 Apr 2008 23:38:17 -0400
Date: Sun, 20 Apr 2008 23:38:17 -0400
To: Jeff Piper <xxxxx@rogers.com>
From: "HostVentrilo.com" <info@hostventrilo.com>
Subject: Ventrilo Server Information
Message-ID: <edee9a956937977bcb723593ae6938a5@www.hostventrilo.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset="utf-8"
Content-Length: 567
My only guess would be the PHP programming of the mailer code?