My Rails 3 application sends out emails in both plain text and HTML formats. I have tested it locally using RoundCube and Squirrel Mail clients and they both display HTML version with images, links, etc. GMail on the other hand chooses plain text format. Any idea what's causing this?
Delivered-To: test@gmail.com
Received: by 10.42.166.2 with SMTP id m2cs16081icy;
Thu, 3 Mar 2011 17:01:48 -0800 (PST)
Received: by 10.229.211.138 with SMTP id go10mr1544841qcb.195.1299200507499;
Thu, 03 Mar 2011 17:01:47 -0800 (PST)
Return-Path: <info@example.com>
Received: from beta.example.com (testtest.test.com [69.123.123.123])
by mx.google.com with ESMTP id j14si1690118qcu.136.2011.03.03.17.01.46;
Thu, 03 Mar 2011 17:01:46 -0800 (PST)
Received-SPF: neutral (google.com: 69.123.123.123 is neither permitted nor denied by best guess record for domain of info@example.com) client-ip=69.123.123.123;
Authentication-Results: mx.google.com; spf=neutral (google.com: 69.123.123.123 is neither permitted nor denied by best guess record for domain of info@example.com) smtp.mail=info@example.com
Received: from localhost.localdomain (localhost [127.0.0.1])
by beta.example.com (Postfix) with ESMTP id F3C273A3EC
for <test@gmail.com>; Fri, 4 Mar 2011 01:01:45 +0000 (UTC)
Date: Fri, 04 Mar 2011 01:01:45 +0000
From: info@example.com
To: test@gmail.com
Message-ID: <4d7039f9e9d3e_3449482ab7831658@test.mail>
Subject: Your example account was activated.
Mime-Version: 1.0
Content-Type: multipart/alternative;
boundary="--==_mimepart_4d7039f9e6967_3449482ab7831370";
charset=UTF-8
Content-Transfer-Encoding: 7bit
----==_mimepart_4d7039f9e6967_3449482ab7831370
Date: Fri, 04 Mar 2011 01:01:45 +0000
Mime-Version: 1.0
Content-Type: text/html;
charset=UTF-8
Content-Transfer-Encoding: 7bit
Content-ID: <4d7039f9e95ed_3449482ab7831519@test.mail>
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
</head>
<body>
<p><a href="http://example.com/"><img border="0" src="http://example.com/images/logo.png" alt="example logo" /></a></p>
<p>Congratulations, Test!</p>
<p>
Your <a style="text-decoration:none;color:#ef4923;" href="http://example.com/">example</a> account was activated.
</p>
</body>
</html>
----==_mimepart_4d7039f9e6967_3449482ab7831370
Date: Fri, 04 Mar 2011 01:01:45 +0000
Mime-Version: 1.0
Content-Type: text/plain;
charset=UTF-8
Content-Transfer-Encoding: 7bit
Content-ID: <4d7039f9e8b0e_3449482ab78314b7@test.mail>
Congratulations, Test!
Your example.com account was activated.
----==_mimepart_4d7039f9e6967_3449482ab7831370--
Try switching the order of the parts of the message, putting the HTML part after the plain-text part. It might work :).
NOTE: I cannot remember now where I read this (or if I for sure even did), but the reason switching might help is because I think the preferred part of the message may be the last part.
Update: I found a place where it says that parts in a multipart MIME message should be in order of increasing preference -- here, in section 7.2.3 (edit: latest version here; thanks @ALEXintlsos!), starting with the third to last paragraph.
Update: Here is a quote of section 7.2.3, (see https://stackoverflow.com/help/referencing):