I'm running BIND 9.3.3rc2 on a CentOS 5 system acting as an SMTP server. Until last week, I haven't had any problems with DNS or name resolution. The only problems I have resolving are with subdomains for Microsoft's Outlook 365 service.

For our customers who are using Outlook 365, Microsoft has changed their MX server configuration from a generic mail.outlook.com domain to example-com.mail.eo.outlook.com where 'example-com' represents their registered domain (they change the dot to a dash). Sometimes 'eo' becomes 'protection' in this scheme. When a customer has an email at one of these subdomains, our SMTP can't resolve the name and the mail goes into the mailq.

If I run dig example.com MX I get the following as output:

example.com    3600  IN  MX  10  example-com.mail.eo.outlook.com

So it finds Microsoft's subdomain for this customer, but I can't ping it or the root domain; they both return

ping: unknown host example-com.mail.eo.outlook.com

However if I dig this domain using Google's DNS server, I do get an IP address:

dig example-com.mail.eo.outlook.com @

example-com.mail.protection.outlook.com. 9 IN A
example-com.mail.protection.outlook.com. 9 IN A

I can statically add those entries to /etc/hosts, but this means being reactive. How do I need to configure DNS so that these entries will work? If they work for Google they must work for others as well.

  • What is the output of the following commands? cat /etc/resolv.conf & dig example.com MX +trace – Chris Davidson Dec 22 '14 at 6:06
  • @Dayvo, I found out what the problem was partially. /etc/resolv.conf only had as its nameserver. I don't know why the local DNS records haven't been updated, but I added our ISP's DNS server to nameserver and restarted named. – Tensigh Dec 24 '14 at 0:31
  • 1) Provide the real names if you want help. 2) a record can have a MX resource type attached to it (so that it will handle email reception) but not have an A/AAAA record so that ping or any other tool on it will fail – Patrick Mevzek Apr 14 '18 at 22:05

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