Hello,

My company has been running an Exchange 2013/2010 coexistence. Currently, Exch 2013 (2mbx and 1 CAS) utilizes "mail2.domain.com" for the name space. Exch 2010 (1MBX 1 CAS) uses "mail.domain.com"

We recently attempted to cutover external and internal DNS to point "mail.domain.com" and "autodiscover.domain.com" to the Exch 2013 server. 

We changed all virtual directories on 2013 to use "https://mail.domain.com/owa" (ECP, EWS, etc. were changed too) for the internal and external URL. The Exch 2010 virtual directories internal URL are set to "https://internalFQDN.domain.com/owa" the external URLs are $null

Both CAS servers were setup to use Outlook Anywhere since this is how 2013 proxies to 2010. The internal URLs for both were set to "mail.domain.com" IIS authentication Methods (Basic, NTLM). ClientAuthenicsationMethod: NTLM.

For both servers the autodiscoverserviceinternaluri was set to: https://autodiscover.domain.com/autodiscover/autodiscover.xml

The 2013 server has two SSL certificates installed. One is a wildcard cert for "*.domain.com" and the other includes our SANs (mail.domain.com, mail2.domain.com, webmail.domain.com, autodiscover.domain.com) it also includes the FQDN for the 2010 and 2013 CAS servers.

I'm speaking in the past tense because we had to roll back. The problem was no Outlook user could connect. This goes for mailboxes hosted on the Exchange 2013 and 2010 servers. The error was: "Cannot open your default e-mail folder" to "The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete".

Everything else worked fine during the cutover. OWA 2013 login page proxied 2010 logins properly, Outlook 2011 could connect with EWS fine, Active-Sync worked without issues too. It was only the Outlook 2010 and 2013 clients that could not connect.

We rolled back and everything is working as it was before with the separate namespace. That leads me to think it's something with Outlook Anywhere (RPC/HTTPS) but the settings seem correct unless I'm missing something. Any help is appreciated.

Thanks!

Hi,

According to your description, I understand that Outlook 2010 and Outlook 2013 client cannot connect to Exchange server after cutover namespace in coexistence environment, however EWS, OWA and ActiveSync works fine.
If I misunderstand you concern, please do not hesitate to let me know.

I want to double confirm some question, please help to collect answers for below question:
1. Whether all account or just user in Exchange 2010 experience this question.
2. Run Get-ExchangeCertificate | FL Identity,Services,Subject command to double check the certificate for Exchange server.
3. Ensure the DNS record for Exchange server, we may need DNS record both Exchange 2013 and Exchange 2010.

Also, please use Microsoft Remote Connectivity Analyzer(https://testconnectivity.microsoft.com/) to test the connectivity for RPC over HTTP.
Additional, heres an blog about the coexistence configuration when migrate Exchange 2007 to Exchange 2013, for your reference:
http://blogs.technet.com/b/meamcs/archive/2013/07/25/part-2-step-by-step-exchange-2007-to-2013-migration.aspx

Thanks

Thanks for the response Allen.

1. All accounts experienced the issue, those on Exch 2010 and 2013.

2. I verified both CAS servers have the certificate installed.

3. DNS was setup properly at the time, it's hard for me to test that again since these are production systems.

4. I ran the remote connectivity analyzer during the troubleshooting and did receive errors for RPC/HTTPS. Autodiscover passed and it was able to find the DNS records which kind of left me at a loss.

We're thinking about rolling out Exch 2013 under the "webmail" namespace and leave 2010 just "mail" it's working properly right now with using "mail2" for Exch 2013. This will not be as seamless to the user, they will need to restart Outlook and enter credentials once if they're using Outlook at the time of migration. We'll have to announce the new OWA URL too. Those hurdles aren't as big of a problem since we're still a smaller organization with about 400 users and we can manage the migration process.

Please let me know if you have any other ideas or suggestions.