My program sends daily emails to users. I recently switched servers and once we setup the email job on the new server, one of our users complained that they are receiving the email in plan text. No other user has this problem.
The header that most users receive is as follows (replaced sensitive info with <> tags):
Delivered-To: <email> Received: by 10.229.215.75 with SMTP id hd11cs31754qcb; Fri, 8 Jul 2011 06:00:20 -0700 (PDT) Received: by 10.150.236.18 with SMTP id j18mr2060469ybh.84.1310130019825; Fri, 08 Jul 2011 06:00:19 -0700 (PDT) Return-Path: <return path> Received: from <server> ([<ip address>]) by mx.google.com with ESMTP id f14si8302490ybc.25.2011.07.08.06.00.18; Fri, 08 Jul 2011 06:00:18 -0700 (PDT) Received-SPF: neutral (google.com: <ip address> is neither permitted nor denied by best guess record for domain of <return path) client-ip=<ip address>; Authentication-Results: mx.google.com; spf=neutral (google.com: <ip address> is neither permitted nor denied by best guess record for domain of <return path>) smtp.mail=<return path> Received: by <server name> (Postfix, from userid 1001) id 41B4C162FFA; Fri, 8 Jul 2011 08:00:17 -0500 (CDT) To: <user email address> Subject: <subject> X-PHP-Originating-Script: 33:Email.php From: <from email address> Content-Type: text/html; charset=utf-8 Message-Id: <20110708130018.41B4C162FFA@<server>> Date: Fri, 8 Jul 2011 08:00:17 -0500 (CDT)
However, the user with the errors receives the following header:
Return-Path: <return path> Received: from <server> (UnknownHost [<ip address>]) by seriousw1.seriousw1.com with SMTP; Mon, 11 Jul 2011 08:00:26 -0500 Received: by <server> (Postfix, from userid 1001) id 72F2A163F34; Mon, 11 Jul 2011 08:00:09 -0500 (CDT) To: <user email address> Subject: <subject> X-PHP-Originating-Script: 33:Email.php From: <from email> Message-ID: <809141a1b4f842e0a015f20c000dab91@com> X-SmarterMail-Spam: SPF_None, Reverse DNS Lookup, ISpamAssassin 3 [raw: 2], DK_None, DKIM_None X-SmarterMail-TotalSpamWeight: 5
As you can see above, the Content-Type declaration is not contained within the second header, resulting in the message being interpreted as plain text.
I have tried various things but am now completely stuck. Any help or thoughts are much appreciated.