about two weeks ago I had security breach, one mail account on server, caused outgoing spam, I got listed in on couple blacklists rbl. Problem was fixed, IP was removed from all black lists. I can't still mail to google servers (gmail 550-5.7.1 likely unsolicited mail). Problem applies only one of domains on server, from rest domains on the same machine, mails are delivering without problems to gmail servers. Look this, test from one server, outgoing mail from two domains:
Reporting-MTA: dns; ns3481305.ip-176-31-231.eu X-Postfix-Queue-ID: 2CC23222C6 X-Postfix-Sender: rfc822; redakcja@gornicza.com.pl Arrival-Date: Mon, 30 Jan 2017 07:56:39 +0100 (CET)
Final-Recipient: rfc822; ….com Original-Recipient: rfc822;… Action: failed Status: 5.7.1 Remote-MTA: dns; gmail-smtp-in.l.google.com Diagnostic-Code: smtp; 550-5.7.1 [2001:41d0:2:f8eb:: 12] Our system has detected that this message 550-5.7.1 is likely unsolicited mail. To reduce the amount of spam sent to 550-5.7.1 Gmail, this message has been blocked. Please visit 550-5.7.1 more information. k46si15331100wrk.55 – gsmtp
Second test from same server, mail delivered no problem:
Delivered-To: … Received: by 10.12.180.171 with SMTP id c43csp1297317qve; Mon, 30 Jan 2017 00:05:23 -0800 (PST) X-Received: by 10.28.178.142 with SMTP id b136mr13272598wmf.69.1485763523027; Mon, 30 Jan 2017 00:05:23 -0800 (PST) Return-Path: Received: from ns3481305.ip-176-31-231.eu ([2001:41d0:2:f8eb::]) by mx.google.com with ESMTP id m15si12383431wmh.131.2017.01.30.00.05.22 for ; Mon, 30 Jan 2017 00:05:22 -0800 (PST) Received-SPF: pass (google.com: domain of test@nettg.pl designates 2001:41d0:2:f8eb:: as permitted sender)
Server is not currently blacklisted: http://www.anti-abuse.org/multi-rbl-check-results/?host=176.31.231.235 http://mxtoolbox.com/SuperTool.aspx?action=blacklist:176.31.231.235
SPF, DKIM and rDNS are configured, everything worked while got security breach and spam accident.
Best Answer
Sending the email to google user is always be a challenge, out of 1000+ factors Gmail mainly consider the sending domain and IP reputation. You have to build a good reputation in front of Gmail. Please be remember for Gmail It doesn't matter whether your sending IP is listed in Spamhaus or any other major DNSBL.
It's all about reputation and to build the reputation you have to send a good email. Google always loves email replies so ask or encourage your users to reply your email.
One thing I have noticed that the IP -176.31.231.235 doesn't seem to be have standard PTR. rDNS for IP 176.31.231.235 ns3481305.ip-176-31-231.eu reference - http://multirbl.valli.org/lookup/176.31.231.235.html
I strongly recommend changing the rDNS of this IP from generic to a specific one. Also, please add Google TXT record in your domain's DNS so that you can be aware of what is happening with your domain and IPs. Google postmaster dashboard also provide other useful metrics. https://postmaster.google.com/
Hope this helps...