I configured postfix on snow leopard by adding the following line to /etc/hostconfig:

MAILSERVER=-YES-

I then configured postfix to relay through my ISP's SMTP server. I added the following two lines in their respective places within /etc/postfix/main.cf:

myhostname = 1and1.com
relayhost = shawmail.vc.shawcable.net

I then have a simple PHP mail function wrapper as follows:

send_email("[email protected]", "[email protected]", "Test Email", "<p>This is a simple HTML email</p>");
echo "Done";

function send_email($from,$to,$subject,$message){
 $header="From: <".$from.">
";
 $header.= 'MIME-Version: 1.0' . "
";
 $header.= 'Content-type: text/html; charset=iso-8859-1' . "
"; 
 $send_mail=mail($to,$subject,$message,$header);
 if(!$send_mail){ echo "ERROR"; }
}

With this, I am receiving an e-mail that appears to be improperly formatted. The message header is showing up in the body of the e-mail. The raw message content is as follows:

Return-Path: <[email protected]>
Delivery-Date: Tue, 27 Apr 2010 18:12:48 -0400
Received: from idcmail-mo2no.shaw.ca (idcmail-mo2no.shaw.ca [64.59.134.9])
 by mx.perfora.net (node=mxus2) with ESMTP (Nemesis)
 id 0M4XlU-1NCtC81GVY-00z5UN for [email protected]; Tue, 27 Apr 2010 18:12:48 -0400
Message-Id: <[email protected]>
Received: from pd6ml3no-ssvc.prod.shaw.ca ([10.0.153.149])
  by pd6mo1no-svcs.prod.shaw.ca with ESMTP; 27 Apr 2010 16:12:47 -0600
X-Cloudmark-SP-Filtered: true
X-Cloudmark-SP-Result: v=1.0 c=1 a=VphdPIyG4kEA:10 a=hATtCjKilyj9ZF5m5A62ag==:17 a=mC_jT1gcAAAA:8
 a=QLyc3QejAAAA:8 a=DGW4GvdtALggLTu6w9AA:9 a=KbDtEDGyCi7QHcNhDYYwsF92SU8A:4
 a=uch7kV7NfGgA:10 a=5ZEL1eDBWGAA:10
Received: from unknown (HELO 1and1.com) ([24.84.196.104])
  by pd6ml3no-dmz.prod.shaw.ca with ESMTP; 27 Apr 2010 16:12:48 -0600
Received: by 1and1.com (Postfix, from userid 70)
 id BB08D14ECFC; Tue, 27 Apr 2010 15:12:47 -0700 (PDT)
To: [email protected]
Subject: Test Email
X-PHP-Originating-Script: 501:test.php
Date: Tue, 27 Apr 2010 18:12:48 -0400
X-UI-Junk: AutoMaybeJunk +30 (SPA);
  V01:LYI2BGRt:7TwGx5jxe8cylj5nOTae9JQXYqoWvG2w4ZSfwYCXmHCH/5vVNCE
  fRD7wNNM86txwLDTO522ZNxyNHhvJUK9d2buMQuAUCMoea2jJHaDdtRgkGxNSkO2
  v6svm0LsZikLMqRErHtBCYEWIgxp2bl0W3oA3nIbtfp3li0kta27g/ZjoXcgz5Sw
  B8lEqWBqKWMSta1mCM+XD/RbWVsjr+LqTKg==
Envelope-To: [email protected]

From: <[email protected]>
MIME-Version: 1.0
Content-type: text/html; charset=iso-8859-1
Message-Id: <[email protected]>
Date: Tue, 27 Apr 2010 15:12:47 -0700 (PDT)


<p>This is a simple HTML email</p>

And here are the contents of my /var/log/mail.log file after sending the email:

Apr 27 15:29:01 User-iMac postfix/qmgr[705]: 74B1514EDDF: removed
Apr 27 15:29:30 User-iMac postfix/pickup[704]: 25FBC14EDF0: uid=70 from=<_www>
Apr 27 15:29:30 User-iMac postfix/master[758]: fatal: open lock file pid/master.pid: unable to set exclusive lock: Resource temporarily unavailable
Apr 27 15:29:30 User-iMac postfix/cleanup[745]: 25FBC14EDF0: message-id=<[email protected]>
Apr 27 15:29:30 User-iMac postfix/qmgr[705]: 25FBC14EDF0: from=<[email protected]>, size=423, nrcpt=1 (queue active)
Apr 27 15:29:30 User-iMac postfix/smtp[747]: 25FBC14EDF0: to=<[email protected]>, relay=shawmail.vc.shawcable.net[64.59.128.135]:25, delay=0.21, delays=0.01/0/0.1/0.1, dsn=2.0.0, status=sent (250 ok:  Message 25784419 accepted)
Apr 27 15:29:30 User-iMac postfix/qmgr[705]: 25FBC14EDF0: removed

Two other people in the office have followed the exact same process and are running the exact same script, version of snow leopard, php, etc. and everything is working fine for them. I've even copied their config files to my machine, restarted postfix, restarted apache, all to no avail.

Does anyone know what steps I could take to resolve the issue? This is boggling my mind...

Thanks