Some mailboxes cannot connect using Outlook

[disturbedone]

Exchange 2010 SP2 with ~2000 mailboxes. Our SAN filled up for an unknown reason last week and several VMs stopped working. whatever caused it to fill up disappeared and the space was then available. Simply accepting the problem in vSphere made the VMs resume and largely there hasn't been an issue since.

Two of the VMs that were affected were one of the two CA/HT servers and one of the two MBX servers. I restarted all servers and most issues with Outlook disappeared.

But a handful of users have since reported multiple issues. The main one is that Outlook will give the 'The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action." and then 'The name cannot be resolved. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.". These users can access OWA without issue and also ActiveSync on mobile devices still works. The issue is present when the user logs on to different computers.

I've checked ADSI Edit and there's nothing obviously missing/wrong compared to working users.

Any ideas what has caused this and how to resolve it?

 

[disturbedone]

I found this

http://www.msoutlook.info/question/531

and added the registry key and it resolved all issues with Outlook.

Why it only affected a handful of users I don't know. It looks like one of the DCs may have got messed up after the outage so I'll reboot it tonight as the registry key should not be required.

 

[disturbedone]

Rebooting the DC and removing the registry key causes the fault to return. This is occurring for ~6 out of ~1500 users (that I know of). Both DCs are listed as GC servers in AD Sites & Services. There are no old NS/SRV records in DNS like the linked article suggests might be the cause and this only occurred after the issue on Thur night.

Any ideas why and/or how to fix it without this registry entry?

 

[ShackDaddy]

I would be focusing on the health of your AD. Since not using the registry key replicates the issue, can you check the Directory Services logs on all your GC's and do repadmin /showreps on all DCs to make sure you don't have one in USN rollback mode?

I'm not sure why so few of your clients are having the issue, but it sounds like the root problem is that they are querying for data from the AD and are not able to retrieve it unless they are told specifically to connect to a known healthy GC. That indicates that something's not right in the AD environment.

Dave Shackelford
ThirdTier.net
TrainSignal.com