I am getting double e-mails in Horde as well (didn't think I was).
Here are the headers of the 2 e-mails
e-mail 1
Return-Path: <henry@mrlistersir.com>
Delivered-To: henry44@henry.alpinepump.com
Received: (qmail 4812 invoked by alias); 5 Sep 2009 03:51:58 -0000
Delivered-To: alias-localdelivery-henry44@alpinepump.com
Received: (qmail 4809 invoked by uid 453); 5 Sep 2009 03:51:58 -0000
X-Virus-Checked: Checked by ClamAV on alpinepump.com
X-Spam-Status: No, hits=0.0 required=5.0
tests=
X-Spam-Check-By: alpinepump.com
Received: from larry-server.mrlistersir.com (HELO mrlistersir.com) (207.55.114.23)
by alpinepump.com (qpsmtpd/0.40) with SMTP; Fri, 04 Sep 2009 20:51:54 -0700
Received: (qmail 11361 invoked by uid 453); 5 Sep 2009 03:51:53 -0000
X-Virus-Checked: Checked by ClamAV on mrlistersir.com
Received: from lenny.mrlistersir.com (HELO [127.0.0.1]) (192.168.1.249)
by mrlistersir.com (qpsmtpd/0.40) with ESMTP; Fri, 04 Sep 2009 20:51:52 -0700
Message-ID: <4AA1E059.1080300@mrlistersir.com>
Date: Fri, 04 Sep 2009 20:51:53 -0700
From: Henry Gillow-Wiles <henry@mrlistersir.com>
User-Agent: Thunderbird 2.0.0.23 (Windows/20090812)
MIME-Version: 1.0
To: henry44@alpinepump.com
Subject: test1
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
e-mail 2
Return-Path: <henry@mrlistersir.com>
Delivered-To: henry44@henry.alpinepump.com
Received: (qmail 4812 invoked by alias); 5 Sep 2009 03:51:58 -0000
Delivered-To: alias-localdelivery-henry44@alpinepump.com
Received: (qmail 4809 invoked by uid 453); 5 Sep 2009 03:51:58 -0000
X-Virus-Checked: Checked by ClamAV on alpinepump.com
X-Spam-Status: No, hits=0.0 required=5.0
tests=
X-Spam-Check-By: alpinepump.com
Received: from larry-server.mrlistersir.com (HELO mrlistersir.com) (207.55.114.23)
by alpinepump.com (qpsmtpd/0.40) with SMTP; Fri, 04 Sep 2009 20:51:54 -0700
Received: (qmail 11361 invoked by uid 453); 5 Sep 2009 03:51:53 -0000
X-Virus-Checked: Checked by ClamAV on mrlistersir.com
Received: from lenny.mrlistersir.com (HELO [127.0.0.1]) (192.168.1.249)
by mrlistersir.com (qpsmtpd/0.40) with ESMTP; Fri, 04 Sep 2009 20:51:52 -0700
Message-ID: <4AA1E059.1080300@mrlistersir.com>
Date: Fri, 04 Sep 2009 20:51:53 -0700
From: Henry Gillow-Wiles <henry@mrlistersir.com>
User-Agent: Thunderbird 2.0.0.23 (Windows/20090812)
MIME-Version: 1.0
To: henry44@alpinepump.com
Subject: test1
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
I can't see any differences in the message id's or other aspects of the e-mails.