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We have one client with 3 domains and we send regular emails to all 3 of them. Email to these domains were sent succesfully without hitch for a number of year and only recently are failing with hostname unresolved delivery reports.

No other outgoing emails to any other address are failing just the 3 specific client domains.

I have run mx record checks and they are somewhat like the following

domainA.com mx record :mxa-hosted.com ip: 123.123.123.1 :mxb-hosted.com ip: 123.123.123.2

domainB.com mx record :mxa-hosted.com ip: 123.123.123.1 :mxb-hosted.com ip: 123.123.123.2

domainC.com mx record record :mxa-hosted.com ip: 123.123.123.2 :mxb-hosted.com ip: 123.123.123.1

MX Records for all 3 domains point to the same mailserver(relay?) but domainC.com has the two mailserver ip addresses swapped around. Could this be causing the error?

Traceroute on the three domain names fail as well, gets to 15 hops and wont progress from there. I am trying to rule out our having a problem, I dont think its our side as all other email is getting where it needs to go.

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  • can you had the relevant SMTP logs ?
    – JFL
    Feb 29, 2016 at 11:49
  • Supersecret domains? Can you share the actual domains? Are you able to deliver email to them through other mailservers, eg. Office 365, Gmail? Can Mxtoolbox connect to them? Feb 29, 2016 at 13:11
  • Not too secret, estee.com and estee-lauder.co.uk Mar 2, 2016 at 12:37
  • mxtoolbox has mixed results. Cant connect to SMTP server through MXToolbox but can deliver email through gmail. I have added host table entries to resolve directly to mailserver ip and that works for now but not ideal. Mar 2, 2016 at 12:39
  • I'm a bit busy at the moment, but if MXToolbox has issues with their setup I'd be inclined to agree with the toolbox that the recipient has munged their MX configuration. Mar 4, 2016 at 11:07

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