How to avoid being marked as spam with custom mail server?

Question

As of late, maybe during the past few months, Googlemail started flagging/marking mails coming from my domain as spam. I am running a postfix/amavisd (clamav and spamassassin) combination that is configured quite rigidly so I hardly see any spam in my own inbox. I am using SPF, DMARC, DKIM, don't allow relay access, don't do any header rewriting and my IP is not on any blacklists. Reverse DNS etc is set up and working fine. Also, in essence, I only have one user (me).

I have noticed that my mail is delivered properly (no SMTP errors whatsoever) but is immediately marked as spam and moved to the spam folder of any 'new' Googlemail inbox that I'm sending to. Now, by nature of my business, it happens from time to time that I have to send mails to clients that I have never mailed before. I cannot possibly call every single one before sending them a mail and ask them to check their spam folder... Also I use several "from" addresses on my domain, i.e. sending mails from sales@ as well as info@. When info@ is marked as "non spam" in Googlemail mails from sales@ are still being delivered directly to the spam folder so not even this works for me. When looking at the header fields in the received mails, there is only "pass"/"ok" and no mention of "failed".

I tried contacting Google via their various web forms and also added a Google site verification TXT record in my DNS entries but to no avail. Not even a response.

The same thing happens for Hotmail/live/outlook.com inboxes where mails from my domain are immediately moved to the spam folder. Problem here is that there doesn't even seem to be a way to contact Microsoft to address these kinds of problems.

So, is there anything else I can do? Other things I should check? Do you know of any contact addresses I could write to? Any last resorts to try?

In its current state, my mailserver is essentially useless and I'd argue if the situation doesn't improve the whole email system is doomed. If no one can host their own mailserver anymore we can all just as well go to Google, Microsoft or Facebook and hand them over our data (which we are already doing anyway). If the old, federated mail system is not working, in my opinion, there is no need for email anymore and we could resort to Facebook messages, whatsapp and the likes. I don't know if this is in Google's interest, but well...

Adding a recent mail as received my Googlemail:

Received-SPF: pass (google.com: domain of postmaster@mydomain.com designates myip as permitted sender) client-ip=myip;
Message-ID: <55B33DFD.9090805@mydomain.com>
Date: Sat, 25 Jul 2015 09:42:53 +0200
From: "postmaster@mydomain.com" <postmaster@mydomain.com>
User-Agent: myuseragent
MIME-Version: 1.0
To: mygmail@gmail.com
Subject: test16
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

test16 this is another test to see if gmail still considers mails from my domain
spam.

Nominating to close as off-topic because this is a site for progamming questions, not email deliverability questions. — tripleee, Jul 25 '15 at 08:54
Without seeing a sample email, there' not much we can suggest. My only suggestion would be to make your email as short as possible. 1 sentence with a link to the rest of the information would be ideal. — Gilbert Le Blanc, Jul 25 '15 at 09:05
Added a sample email, as you can see, it already is quite short. — Sonny O'Rullivan, Jul 25 '15 at 16:40
One tip. Please simplify your answer and utilize **bold**, *italic* and other typographic technique to improve readability. — Daniel Cheung, Feb 19 '17 at 01:35

score 2 · Answer 1 · answered Jul 25 '15 at 18:01

Without seeing full headers (including domains and IPs) it's hard to say for sure.

However, where do you host your server? If you're in known IP space for something like linode, digitalocean, beyondhosting, you may be sitting in an IP block with poor reputation. I assume you have checked your IP against all major blacklists, but even if it's not blacklisted specifically it may be an untrusted netblock.

(this should have been a comment, but I apparently can't make one)

score 1 · Answer 2 · edited Apr 20 '17 at 16:26

It may be because you are sending from postmaster@mydomain.com. postmaster is an admin email for receiving complaints and not for sending email. Google might pass your SPF and DKIM, but still consider you spam based on its own criteria (like its own SpamAssassin). I'm able to send myself an email to GMail and I'm also passing SPF and DKIM. I don't send from postmaster though. You can use http://www.kitterman.com/spf/validate.html to test your SPF and send a message to check-auth@verifier.port25.com to verify your DKIM & SPF. Google might have its own private blacklist of IP addresses to based on prior history before you took it over.

score 1 · Answer 3 · answered Feb 18 '17 at 17:35

Google and Microsoft disclose some information about their internal reputation metrics.

In order to access such information you need to subscribe the following services: google: https://postmaster.google.com microsoft: https://postmaster.live.com/snds/

You may also want to check your postfix logs. When the reputation is low some messages will receive a "defer" smtp rejection. The last message of such smtp transactions may provide clues about why your reputation is low.

Check your postfix configuration in respect to destination concurrency limit and destination rate delay. Use polite settings.

They also don't like spikes of email flow, you may want to rate-limit your mail flow towards the domains hosted by them.

How to avoid being marked as spam with custom mail server?

3 Answers3