5

Several emails sent from my webserver to a Gmail address, where the From: address is websitevisitor@gmail.com, have been marked as spam by Gmail. The From: field is populated from form data, and corresponds to the visitor's actual email address, which often is a Gmail address. The Return-Path: is always pointing to an address account@mywebserver.com, which means that SPF and DKIM checks will work.

When I inspect the raw emails in the Gmail account, I see the following:

Delivered-To: webformrecipient@gmail.com
...
Return-Path: <account@mywebserver.com>
Received: from mywebserver.com (mywebserver.com. [my:ipv6:address])
        by mx.google.com with ESMTPS id xxx
        for <webformrecipient@gmail.com>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Tue, 02 Feb 2016 00:40:02 -0800 (PST)
Received-SPF: pass (google.com: domain of account@mywebserver.com designates my:ipv6:address as permitted sender) client-ip=xxx;
Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of account@mywebserver.com designates my:ipv6:address as permitted sender) smtp.mailfrom=account@mywebserver.com;
       dkim=pass header.i=@mywebserver.com;
       dmarc=fail (p=NONE dis=NONE) header.from=gmail.com
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mywebserver.com; s=mydkim;
    h=Date:Message-Id:Sender:From:Subject:To; bh=w2snQznwxlVRVACmfQELC7VGmD1dcYdiCXbCIRYFKRs=;
    b=a0Vy3Ky43J5FdiWSuQ4qvTTH47G+Js0W/qtRU5gMlxfesNqrlyaIyExaIZlWvHNL4o0LNOF1GI94w4C41mmH+2JIkMEQZazw0MainP7UyUgsm/RZbAWoRuecPv+k108FlsWMP/l1UttXAdlvBVJmV2UGsYYlSSjKErQEF8tv3K0=;
Received: from apache by mywebserver.com with local (Exim 4.80)
    (envelope-from <account@mywebserver.com>)
    id 1aQWVF-00009b-2X
    for webformrecipient@mywebserver.com; Tue, 02 Feb 2016 09:40:01 +0100
To: webformrecipient@mywebserver.com
From: Website User <website-user@gmail.com>
Sender: webformrecipient@mywebserver.com
...

Note that both the SPF and DKIM checks are passing, but the DMARC check is not. After some searching, I tracked this down to DMARC using the From: address to get its reference domain from, according to this answer on stack overflow.

Three questions:

  1. Is it likely that indeed the dmarc=fail is the cause of the email being assigned to spam by Gmail?
  2. Why does DMARC operate on the From: address, rather than the Return-Path (envelope sender) as SPF and DKIM do?
  3. If now also the From: header has to correspond to an address @mydomain.com then how should we specify the actual (logical, flesh and blood) sender of the message?
6

Think of SPF and DKIM as ways to validate the mail path, and think of DMARC as an extension that also validates the message sender. Think of this as delivering a FedEx letter. It's easy to validate where the envelope was shipped from, and that the courier was legitimate, but it doesn't provide a way to prove that the letter inside the envelope is really from the person whose name is printed on it.

Your webserver is a valid SMTP server for mywebserver.com and that your Sender address is legitimate, but that's not enough for other servers to trust that you have permission to send as website-user@gmail.com . How does GMail know that your server hasn't been hacked or otherwise used for malicious intent? Gmail's servers aren't going to blindly trust you to send mail as one of their users -- unless maybe you are hosted by them, and then you'd probably have trouble sending to Yahoo.

To address your first part of the question, yes, it's very likely that this is why GMail is categorizing it as spam. The oldest forms of spam center around spoofing the "From" address. This is what most users see when they get a message, and is the primary field they want to trust. When a message from a legitimate mail server is sent using a From address that doesn't belong to that mail server, it's still a red flag.

As you mentioned, DMARC operates on the From address as part of the specification. Granted, it makes it harder to write web apps that send on someone's behalf, but that's sort of the point. As to why they do it - well, that's up to the designers of the specification, but it's a trade-off. They are taking the high road and making a system that works very well if you stay within that limitation. Perhaps future mechanisms will find a way around this.

The unfortunate solution is to only use addresses that you have control of. To address your third question, sign your messages with your domain name, and mention in the body that it was sent on behalf of website-user@gmail.com. Otherwise you will have to request that your recipients add the address to their whitelist. It's not much fun for a legitimate web app developer, but it will protect the sanctity of the recipient's inbox. You might have luck using the Reply-To header with the web user's email address.

There is a discussion of this limitation on this DMARC thread.

In the mean time, you can try to make sure that your server isn't blacklisted on any RBLs. It could be that you can fail DMARC but still get through some spam filters if you have good enough reputation... but I wouldn't rely on it.

2

1) yes, likely the dmarc failure will cause gmail to junk your mails

2) also would be interested in an answer for this

3) I would (and we do) use the reply-to field for the customer address, our mails look like this:

from: website@mydomain.com

to: user@mydomain.com

subject: contact form

reply to: customer-addy@somewhere.com

Hope this helps

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