We use Mailgun to send out emails and recently I noticed quite a few emails each day are being rejected by Gmail.
Here's the type of message we receive:
550
5.7.1 [184.173.153.6 11] Our system has detected that this message is
5.7.1 not RFC 2822 compliant. To reduce the amount of spam sent to Gmail,
5.7.1 this message has been blocked. Please review
5.7.1 RFC 2822 specifications for more information. f15si23385851vdu.1 - gsmtp
The RFC 2822 spec is a massive document so I haven't read it front-to-back but from looking at resources around the web our emails don't fall into any of the common pitfalls that would trigger this type of response from Gmail.
Here's an example email header:
Received: by luna.mailgun.net with HTTP; Mon, 29 Jun 2015 21:06:59 +0000
Message-Id: <20150629210659.18668.39318@(domain)>
X-Mailgun-Variables: {"variation": "original", "campaign_code":
"(customValue)"}
Reply-To: (name) <(email)>
X-Mailgun-Track: false
X-Mailgun-Tag: (customTag)
To: (email)
From: (name) <(email)>
Subject: (subject)
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="12f0bd630f2145a3afcd98b621a3b1f2"
--12f0bd630f2145a3afcd98b621a3b1f2
Content-Type: text/plain; charset="ascii"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
(text content)
--12f0bd630f2145a3afcd98b621a3b1f2
Content-Type: text/html; charset="ascii"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>(title)</title>
<style type="text/css">
(css)
</style>
</head><body style="(css)" >
(content)
</body>
</html>
--12f0bd630f2145a3afcd98b621a3b1f2--
What are we doing wrong?
It turned out we were using two different domains for the From and Reply-to which I guess is a no-no.