Can anyone tell me why my mail is being classified as spam (headers included)

Question

Here is the situation.

I have both an SMTP server which accepts only authentication.

I also have a VPS with no SMTP server, so the PHP on that VPS sends emails using PEAR to the SMTP server for sending.

For some reason emails are getting classified as Spam always. Can someone take a look at the following headers and give me a pointer to why this might be happening?

Some stuff has been *'d out for security.

I'm new to VPS stuff so I guess I might have some dodgy config somewhere, so I need some advice on this one.

Thanks guys!

Microsoft Mail Internet Headers Version 2.0
    Received: from moutng.k*****.de ([212.227.17.8]) by ***** with Microsoft SMTPSVC(6.0.3790.4675);
         Sat, 12 Feb 2011 11:30:09 +0000
    Received: from localhost (*****.onlinehome-server.info [*****])
        by mrelayeu.k*****.de (node=mreu1) with ESMTP (Nemesis)
        id 0Lm8JB-1QNpTc29Yn-00a9O2; Sat, 12 Feb 2011 12:30:09 +0100
    From: Logeek <log@*****.com>
    To: A King <aking@*****.co.uk>
    Subject: Hi!
    Message-Id: <0Lm8JB-1QNpTc29Yn-00a9O2@mrelayeu.k*****.de>
    Date: Sat, 12 Feb 2011 12:30:09 +0100
    X-Provags-ID: *****
    Return-Path: log@*****.com
    X-OriginalArrivalTime: 12 Feb 2011 11:30:09.0931 (UTC) FILETIME=[34CC45B0:01CBCAA8]

Answer 1

Ok I'm not really good at email headers but if an Email is sent from and address in which the domain is not equal to the domain the email was sent from for example: a message sent by admin@thispage.com from the server otherpage.com will get marked as spam: When using a SMTP server smtp.thispage.com as a local user on that server for example admin@thispage.com the message will be sent from this server and the email wil not be marked as spam. But when sending it as user admin@thispage.com from a different domain using PEAR the message will normally be marked as spam.