I have Exchange(HUB,Mail,CAS) server 2010 running in windows 2012 machine. Active director is running with multiple sites and DCs .

Exchange server is running in one of the AD site and it contain 2 domain controllers and GC enabled on both servers.
These two DC as running as logon server and replication between all domain controller is working fine.

Note : FSMO roles are running different Domain controller and site.


Issue :

The other day, i have restarted one domain controller for monthly windows pathing activity, At that point, none of the clients could attach to Exchange using their Outlook app and one of the computers in the network lost authentication and could not log in. In some instances, sending outgoing worked for the clients still connected to Exchange but all incoming/outgoing mail was stopped.


Post restart exchange server issue got resolved and everything started working.


Question : I would like to know, why exchange server was not lookup for secondary DC or Why second domain controllers was not take over the exchange server when first DC is down.

Do i need to configure any specific configuration in exchange to switch over DC when it is down. i would be VERY appreciative if someone could point me in the right direction...


Note : Static domain controller not configured in Exchange server.

How many DCs you see in MSExchange ADAccess - Event ID 2080 on your exchange server?

Make sure both of DCs are showing up below with correct capabilities

Process xxx.exe (PID=####). Exchange Active Directory Provider has discovered the following servers with the following characteristics:
 (Server name | Roles | Enabled | Reachability | Synchronized | GC capable | PDC | SACL right | Critical Data | Netlogon | OS Version)
In-site:
DC01.domain.com    CDG 1 7 7 1 0 1 1 7 1
DC02.domain.com    CDG 1 7 7 1 0 1 1 7 1

More Reference on these values:  https://support.microsoft.com/en-us/kb/316300 (this KB is for E2003 but gives you info on these)

Hi,

For your question, please refer to below link to get answer:
https://social.technet.microsoft.com/Forums/office/en-US/7e6db41a-4ecf-4ba9-bd82-488b832003c9/some-clients-are-unable-to-use-outlook-when-a-secondary-domain-controller-is-offline?forum=exchangesvrgenerallegacy

Thanks