Hi,
I've done a search before I've posted this and know that the above item risen it's head for multiple reasons previously. I've tried various fixes before posting

Scenario is this. I'm running SME8.1, upgraded from 7.6. We have a catch all account (hosted by 1and1) where all of our mail gets sent and SME is configured using fetchmail in multidrop mode to collect this. SpamAssassin is running along with ClamAV.
Within 8.1 if you send an e-mail to multiple recipients within the company we all get a number of e-mails equal to the number of company recipients. This didn't happen in 7.6, so logically it's related to something in the 8.1 upgrade.
I've watched the process for a test e-mail sent from an external account to me on my work account and my colleague who sits next to me. 1and1 correctly receives two e-mails (one for me, one for my colleague). SME/fetchmail then retrieves both copies and sends each to me and my colleague, resulting in double the number of mails I should receive.
Nothing looks massively remiss, I don't know if it's a configuration issue, software or otherwise. I have configured SME to use the Delivered-To: option
Here is the header of the two e-mails:
Return-Path: <pete@homeserver.com>
Delivered-To: pete@e-smith.workserver.co.uk
Received: (qmail 1015 invoked by alias); 17 Jun 2014 15:18:30 -0000
Delivered-To: alias-localdelivery-pete@workserver.co.uk
Received: (qmail 1010 invoked by uid 453); 17 Jun 2014 15:18:30 -0000
X-Spam-Level: *
X-Spam-Status: No, hits=1.3 required=4.0
tests=RDNS_NONE,SPF_PASS
X-Spam-Check-By: workserver.co.uk
Received: from localhost (HELO e-smith.workserver.co.uk) (127.0.0.1)
by workserver.co.uk (qpsmtpd/0.84) with ESMTP; Tue, 17 Jun 2014 16:18:28 +0100
Received: from pop.1and1.co.uk
by e-smith.workserver.co.uk with POP3 (fetchmail-6.3.6)
Tue, 17 Jun 2014 16:18:28 +0100 (BST)
Received: from www4.homeserver.net ([*.*.*.*]) by mx.kundenserver.de (mxeue105)
with ESMTPS (Nemesis) id 0MQrio-1X9WbZ3c3q-00UM6x for <colleague@workserver.co.uk>;
Tue, 17 Jun 2014 17:18:08 +0200
Received: from localhost ([127.0.0.1]:59202 helo=www4.homeserver.net)
by www4.homeserver.net with esmtpa (Exim 4.82)
(envelope-from <pete@homeserver.com>)
id 1Wwv9A-00068M-LZ; Tue, 17 Jun 2014 11:18:04 -0400
Received: from *.*.*.* ([*.*.*.*])
(SquirrelMail authenticated user pete@homeserver.com)
by www4.homeserver.net with HTTP;
Tue, 17 Jun 2014 11:18:04 -0400
Message-ID: <310922bae960ba5c274bffa4ab44ea59.squirrel@www4.homeserver.net>
Date: Tue, 17 Jun 2014 11:18:04 -0400
Return-Path: <pete@homeserver.com>
Delivered-To: pete@e-smith.workserver.co.uk
Received: (qmail 993 invoked by alias); 17 Jun 2014 15:18:28 -0000
Delivered-To: alias-localdelivery-pete@workserver.co.uk
Received: (qmail 987 invoked by uid 453); 17 Jun 2014 15:18:28 -0000
X-Spam-Level: *
X-Spam-Status: No, hits=1.3 required=4.0
tests=RDNS_NONE,SPF_PASS
X-Spam-Check-By: workserver.co.uk
Received: from localhost (HELO e-smith.workserver.co.uk) (127.0.0.1)
by workserver.co.uk (qpsmtpd/0.84) with ESMTP; Tue, 17 Jun 2014 16:18:26 +0100
Received: from pop.1and1.co.uk
by e-smith.workserver.co.uk with POP3 (fetchmail-6.3.6)
Tue, 17 Jun 2014 16:18:26 +0100 (BST)
Received: from www4.homeserver.net ([*.*.*.*]) by mx.kundenserver.de (mxeue105)
with ESMTPS (Nemesis) id 0M0dhu-1WjELR2ig2-00urF1 for
<pete@workserver.co.uk>; Tue, 17 Jun 2014 17:18:08 +0200
Received: from localhost ([127.0.0.1]:59202 helo=www4.homeserver.net)
by www4.homeserver.net with esmtpa (Exim 4.82)
(envelope-from <pete@homeserver.com>)
id 1Wwv9A-00068M-LZ; Tue, 17 Jun 2014 11:18:04 -0400
Received: from *.*.*.* ([*.*.*.*])
(SquirrelMail authenticated user pete@homeserver.com)
by www4.homeserver.net with HTTP;
Tue, 17 Jun 2014 11:18:04 -0400
Message-ID: <310922bae960ba5c274bffa4ab44ea59.squirrel@www4.homeserver.net>
Date: Tue, 17 Jun 2014 11:18:04 -0400
What is likely to be at fault? Is it fetchmail, qmail or something else?