Gmail and other private servers mark legitimate email as SPAM

The mail server configuration is driving me crazy. Emails sent from my own private server are being banned, again by Gmail and other private servers.

I checked gmail headers and SPF, DKIM and DMARC pass the exam. Attached the headers of a blocked email sent and blocked by gmail (sent to the spam folder)

Received-SPF: pass (google.com: domain of x****@e****a.com designates 62.***.***.202 as permitted sender) client-ip=62.***.***.202;
MIME-Version: 1.0
Content-Type: multipart/alternative;     boundary="=_63e0609e24a7c5c6e72a2b53077f53c2"
Date: Tue, 28 Mar 2017 17:09:02 +0200
From: X*** **** - E*** K*** <x****@e****a.com>
To: t***@gmail.com
Subject: Fwd: Re: --- Subject of the message ---
Organization: E*** K****
In-Reply-To: <9f2d7aa8380dcf31e2a7af4795a1463d@e****a.com>
References: <CAMhvi0=PAuUOpg4eNmYn+gckaRhP6wFMMyO-frJeY5=gPC-qVg@mail.gmail.com> <9f2d7aa8380dcf31e2a7af4795a1463d@e****a.com>
Message-ID: <794731b396abba6212312e17219e6d7f@e****a.com>
User-Agent: Roundcube Webmail/1.1.5

--=_63e0609e24a7c5c6e72a2b53077f53c2
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

--- Here the content of the message ---

--=_63e0609e24a7c5c6e72a2b53077f53c2--

EDIT: Result from senderbase:

Details
IP Address  62.***.***.202
Fwd/Rev DNS Match  Help Yes

Email Reputation  Help  Neutral
Web Reputation  Help    Neutral

Last Day    Last Month
Email Volume  Help  0.0 1.9
Volume Change  Help -100%  ↓    

Hostname    sd-****.h****t.net
Domain  Help    poneytelecom.eu
Network Owner  Help Free SAS
Blacklists  Help
bl.spamcop.net  Not Listed
cbl.abuseat.org Not Listed
pbl.spamhaus.org    Not Listed
sbl.spamhaus.org    Not Listed

Attached the headers of a blocked email sent and blocked by gmail (sent to the spam folder)

If the email wound up in the recipients spam folder then it was in fact not blocked, nor "banned" as you state in your question. It was accepted by Gmail and then categorized as spam either by Gmail's internal spam filter or by the recipient himself/herself. Focus on the content of the message as the likely cause. Your DKIM, SPF, and DMARC are fine, as evidenced in the headers.

Is there any method/rules to check the content of the message? There is really nothing special in it, no attached documents at all. Just a HTML email without any suspicious link (just a mailto and a link to my website), in fact, a very normal business email, communication between two employees.

It could be the fact that the format is HTML or it could be the hyperlinks. Try sending it without the hyperlinks and without any images/signature if they pull content from external sources. If the result is the same then try sending a plain text email as a test.

I marked the reply from joequerty as the solution but I have to say that in the end it did not solve the problem, although it helped so much.

This is how I solved it in case anyone else needs a hand. In order to know what is causing the email to be forwarded to the spam folders, you should add a DMARC record using your postmaster's address so that gmail and other mail providers will send you logs helping you to find out the clue of non-working or bad configured email servers. Once you configure the DMARC, will have to wait, probably hours until your first diagnosis emails arrive. Meanwhile, you can check your settings with mxtoolbox.com and intodns.com tools until you don't get any error. Make sure your SPF and DKIM records (of course DMARC as well) are valid. If after all this steps, your email is still marked as spam you can use the Hotmail (postmaster.live.com) and Gmail (postmaster.google.com) postmaster tools. You will probably need to get a good reputation from them before your emails are delivered to the recipients inbox as they should. Good luck !

Gmail and other private servers mark legitimate email as SPAM

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