They are looking for fully circular DNS and I am surprised you are not having trouble with other large ISP’s.
Circular DNS is defined as: HELO Mailout.yourdomain.com from 192.168.10.1 A record for Mailout.yourdomain.com must be 192.168.10.1 192.168.10.1 must resolve to mailout.yourdomain.com You are connecting from two different IP’s with two different connections, so you can’t meet the above. I don’t know how you do that. But the check I describe is widely in use. I don’t think it is an RFC but have never checked. From: listsad...@lists.myitforum.com [mailto:listsad...@lists.myitforum.com] On Behalf Of Mayo, Bill Sent: Wednesday, February 7, 2018 4:46 PM To: firstname.lastname@example.org Subject: [Exchange] RE: Earthlink Contact? My attempts at postmas...@earthlink.net<mailto:postmas...@earthlink.net> and trou...@earthlink.net<mailto:trou...@earthlink.net> did not work, so I tried the Twitter route. It took a while, but I did ultimately get a response today where they gave me a phone number to call. So, thanks to Michael and everyone else that responded. That said, based on the conversation that I had, I would appreciate a reality check. We have 2 different ISPs and load balance outbound SMTP connections, as well as inbound DNS queries. So, we basically have 2 different IP’s that are used at the edge. We have an MX record that points to the domain name. DNS lookups to that domain name will return one of the 2 IP’s. Both of those IP’s will reverse lookup to the domain name. The HELO/EHLO greeting from the server gives the same domain name as the MX record. Additionally, we have an SPF record that indicates both of those IP’s. What Earthlink seems to be initially suggesting is that they are doing an A record lookup of the domain name and comparing that to the connecting IP address (which seems contrary to the error message). In our setup, this will not always be a match. I can understand that they would do a reverse DNS on the IP to make sure it matches the HELO/EHLO greeting, and I can understand that they might also do an SPF and/or MX lookup to make sure that matches. I don’t understand doing a forward lookup and comparing that to the IP, since I don’t think that having multiple A records for a given domain name is particularly uncommon. Is what they are suggesting a legitimate issue? Bill Mayo From: listsad...@lists.myitforum.com<mailto:listsad...@lists.myitforum.com> [mailto:listsad...@lists.myitforum.com] On Behalf Of Michael B. Smith Sent: Friday, February 02, 2018 10:49 AM To: email@example.com<mailto:firstname.lastname@example.org> Subject: [Exchange] RE: Earthlink Contact? Twitter shame them. @Earthlink and @weCareEarthlink And yes, I’m completely serious. From: listsad...@lists.myitforum.com<mailto:listsad...@lists.myitforum.com> [mailto:listsad...@lists.myitforum.com] On Behalf Of Mayo, Bill Sent: Friday, February 2, 2018 10:16 AM To: email@example.com<mailto:firstname.lastname@example.org> Subject: [Exchange] Earthlink Contact? We are having emails sent to Earthlink being intermittently rejected with the reason “550 ERROR: No or mismatched reverse DNS (PTR) entries”. We have done quite a bit of troubleshooting on this, and the problem does not appear to be on our end. I actually have logs that show 2 consecutive messages where the first one is accepted and the second one rejected. I also see “421 Load too high” messages in the log from Earthlink when these happen. I am trying to figure out how to contact Earthlink to get some assistance, but am striking out with how to contact them. The have a special page if you are getting a “blocked by EarthLink” response, but that doesn’t apply here. There contact page has chat support that requires you to provide an Earthlink account. Does anybody know how to get in touch with someone at Earthlink that could actually help with this problem? Bill Mayo