Mail delayed by several days when sent via VirtualMin (or through Outlook)

Hi I set up VirtualMin on a clean install of Ubuntu 12.04.4 x64 based on the instructions here: https://www.digitalocean.com/community/articles/how-to-install-and-utili...

I am having trouble with sent messages in Outlook or webmail interface failing to arrive at their external email destinations until many days later.

In the Virtualmin post-installation wizard I turned most things off to save RAM. I have since disabled Antivirus and Antispam features to help diagnose.

Outlook is configured as follows: Account type: POP3 Incoming: mail.mydomain.net Outgoing: mail.mydomain.net Username: testmail.serveradmin Outgoing server requires authentication. Using same settings as incoming. Incoming 110, outgoing 25

From this forum I followed instructions to do this: "Also, to make sure that SMTPS and Submission are enabled, you can edit your /etc/postfix/master.cf file, and make sure the lines in there beginning with "Submission" and "SMTPS" are uncommented (along with all the lines following them that begin with "-o". Then restart Postfix after making any changes to those."

I have tried to access mail log files using Filezilla, but when I go to var/log/virtualmin I get 550 Permission Denied, which is odd since I am logged in with the administrator account, and I cannot change permissions on the folder without having permissions to start with.

I also read that there is some kind of log viewer functionality in Virtualmin but under Logs and Reports I only have the following, so I dont know where to go after that: AWstats Configuration, Apache Access Log, Apache Error Log, Logged Webmin Actions, View AWstats Report, Webalizer Report

Here are the mail headers for an example message that took 5 days:

Return-Path: <testmail@mydomain.net>
Delivered-To: cgaxxxxx@optusnet.com.au
Received: from localhost (mydomain.net [107.170.221.247])
    by mail107.syd.optusnet.com.au (Postfix) with ESMTP id 204E4D41FA6
    for <cgaxxxxx@optusnet.com.au>; Thu, 15 May 2014 02:46:25 +1000 (EST)
Received: from CHRISWIN7 (c122-108-176-73.rochd4.qld.optusnet.com.au [122.108.176.73])
    by localhost (Postfix) with ESMTPA id 5A75B24313
    for <cgaxxxxx@optusnet.com.au>; Sat, 10 May 2014 23:23:03 -0400 (EDT)
From: "testmail" <testmail@mydomain.net>
To: "'Chris'" <cgaxxxxx@optusnet.com.au>
References: <008401cf6cc7$0cd856b0$26890410$@gmail.com> <009401cf6cc7$82d19a20$8874ce60$@mydomain.net> <009c01cf6cc8$1a057ce0$4e1076a0$@gmail.com> <00a401cf6cc8$2faed640$8f0c82c0$@optusnet.com.au>
In-Reply-To: <00a401cf6cc8$2faed640$8f0c82c0$@optusnet.com.au>
Subject: RE: I was wondering about the previously discussed items
Date: Sun, 11 May 2014 13:22:47 +1000
Message-ID: <00ac01cf6cc8$4939d6a0$dbad83e0$@mydomain.net>
MIME-Version: 1.0
Content-Type: multipart/alternative;
    boundary="----=_NextPart_000_00AD_01CF6D1C.1AE76D40"
X-Mailer: Microsoft Outlook 14.0
Thread-Index: AQJNmov7gcZLyYgCoaMao3VvFhW7ugFBq93FAttwczsC8rpxYZoF3Kxg
Content-Language: en-us
X-Optus-CM-Score: 0
X-Optus-CM-Analysis: v=2.1 cv=U6SrU4bu c=1 sm=1 tr=0
    a=B/DY8qMWdQvqF1/T82JrRA==:117 a=B/DY8qMWdQvqF1/T82JrRA==:17
    a=U1zVsOOCAAAA:8 a=PO7r1zJSAAAA:8 a=5PKDQJfIiogA:10 a=iqUnrAn9kawA:10
    a=IjZ-PbaXOfgA:10 a=DAwyPP_o2Byb1YXLmDAA:9 a=Zr7miEi8wWIA:10
    a=cKsnjEOsciEA:10 a=pGLkceISAAAA:8 a=u0_-chQyZYUsJ7YSkEYA:9
    a=8zo22MHh2s0QNJV0:21 a=5seVzi3EXQ6gA_To:21 a=CjuIK1q_8ugA:10
    a=V902Kb0jE0MA:10 a=MSl-tDqOz04A:10 a=yMhMjlubAAAA:8 a=SSmOFEACAAAA:8
    a=TXZI5OQ6bRhUQBGtSG8A:9 a=6c20buyhSRILeJ5d:21 a=k70wueHRQlrzE3d3:21
    a=Mc7rGe4SmZxtFdOt:21 a=gKO2Hq4RSVkA:10 a=UiCQ7L4-1S4A:10 a=hTZeC7Yk6K0A:10
    a=frz4AuCg-hUA:10

Any tips would be much appreciated.

Thanks!