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External Autodiscover error Exchange 2010

I have been working with Microsoft to set up a Federation Trust between my company's 4 domains. 2 are Exchange 2010 hosted on-premise, and 2 are seperate tennants in Exchange 365. First they directed me to set up a Hybrid configuration, which did nothing but waste time. After escalating my request, a tech tested everything internally (which I had set up properly from the start), and on the 365 side, only to tell me there was an issue that they couldn't pinpoint and that I should contact the Exchange 2010 support team. I'd rather try with you all first, so here goes:

When I run the Outlook Connectivity test on testconnectivity.microsoft.com I am getting the following errors:

*Testing the SSL certificate to make sure it's valid.
       The SSL certificate failed one or more certificate validation checks.
   >Validating the certificate name.
       Certificate name validation failed.
      >Host name mydomain.com doesn't match any name found on the server certificate CN=css.mydomain.com

*Attempting to test potential Autodiscover URL https://autodiscover.mydomain.com:443/Autodiscover/Autodiscover.xml
       Testing of this potential Autodiscover URL failed.
   > Host autodiscover.mydomain.com couldn't be resolved in DNS InfoDomainNonexistent

*Attempting to contact the Autodiscover service using the DNS SRV redirect method.
   >Attempting to resolve the host name server.mydomain.com in DNS.
      >The host name couldn't be resolved.

In my public DNS, I've just added autodiscover.mydomain.com as an A record, and it is pointing to the same server as my OWA (which works) record ( for this example).

For myself, this is a needle in a haystack kind of problem. I've added the following records in my public DNS:

- autodiscover.mydomain.com IN A
- autodiscover IN CNAME
-_autodiscover._tcp IN SVR 0 443 server.mydomain.com

Using mxtoolbox.com, the CNAME returns autodiscover.mydomain.com  as connected and the IP as

Does anyone see something tragically wrong with what I've done (obviously I've made a mess of this, but please humour me....)?
Philip Thomas
Philip Thomas
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1 Solution
Todd NelsonSystems EngineerCommented:
Connectivity Test...
If you are concerned about the first error in the ExRCA.com test where it errors on the root domain name (mydomain.com) I wouldn't worry about it and it can be disregarded as a red herring.

Autodiscover DNS Records...
IMO, you either use an CNAME record (recommended) or an A record for autodiscover.

The CNAME should be using you OWA FQDN as the target, not an IP address.

Also, I haven't used or needed an SRV record for autodiscover in a long time.  I look at it as a helper if the CNAME isn't working.

Those are my thoughts.
Philip ThomasMIS ManagerAuthor Commented:
Thank you Todd for the help, I've modified my CNAME as you've suggested, hopefully I'll get the results I'm after very soon!
Philip ThomasMIS ManagerAuthor Commented:
Well...that did it! Thank you for your help, Todd, it is greatly appreciated!
Todd NelsonSystems EngineerCommented:
You are most welcome.
Philip ThomasMIS ManagerAuthor Commented:
Hi Todd, I've got another question about this topic. 3 of my 4 companies connect to the Federation Trust. My 4th company has an odd setup I've never seen before and I'm hoping you can help me understand what they've done;

There are 2 domain names of interest: domain.com and domainName.com

The email address is @domainName.com
OWA is accessed using mail.domain.com

Each domains' DNS is hosted by GoDaddy, and all the information pointing to our firewall is on the domain.com side.
On the domainName.com side, all the email records are pointing to GoDaddy's servers, which we do not use at all. There are 2 MX records which point the emails to domainName.cominbound10.mxlogic.net (spam filter).

I'm sure this is another DNS issue, but if you would have any insight as to what I should be looking for it would be greatly appreciated.

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