Hi,

Going from 2010 to 2013. Mailboxes on 2013 working fine. But OWA and EAS is not working for users still on 2010.

OWA logon just says "opening mailbox" and timeing out efter 3-4 minutes.

Same namespace (proxy).

Permissions in IIS check, Firewall check...

Hello

what is the  exchange server 2013 CU level?

Hello

on 2010 owa InternalURL  empty?

Hello,

No its not. It contains the fqd

Hi,

From your description, I would like to clarify the following things for troubleshooting:

1. Make sure that you have created a legacy URL to point to the Exchange Server 2010 CAS server.

2. Add the legacy URL in the external DNS zone.

Here is a helpful thread for your reference.

OWA Coexistence 2007 and 2013 (Note: Though it is Exchange 2007 coexistence with 2013, it is also helpful to Exchange 2010 coexistence 2013)

https://social.technet.microsoft.com/Forums/exchange/en-US/bc6fd22a-f653-49a7-a87d-161a57802fef/owa-coexistence-2007-and-2013?forum=exchangesvrdeploy

Hope this can be helpful to you.

Best regards,

Hi,

Is there any update with your issue?

Best regards,

Hi,

No need for legacy on 2010.

Hi,

Since some users are still on Exchange 2010, you need to create a legacy URL to point to the Exchange 2010 CAS server.

Hope my clarification can be helpful to you.

Best regards,

Hi,

I am just writing to see if you have obtained the opportunity to test the solution.

Best regards,