Outlook 2010 not responding

Event logs are a start at client & server end.
Enabling Outlook logging might help as well.
It could be certificate related, or perhaps a new patch for Outlook causing grieve, which is not uncommon.
Outlook logging & Event logs at both ends would likely shed more light onto the matter.

Please review  event viewer to find root cause also post the critical events .

Hi ,Thanks for your response,
these are all the events occurred during issues

Have you changed any permission ?

No, we haven't done any changes , it was a flip, for some users restarting outlook fixed the issue, for some of them restarting machine fixed the issue.

Thanks,
Dinesh

Hi,
I ran Get-Healthreport cmdlet against the server, all healthsets are in healthy state.

Thanks,

From the events in the logs, Microsoft Availability Services & ActiveSync are throwing errors related to network connectivity often.
Is there a firewall in between? Have you tired disabling firewall on Windows end for testing purposes only (Best to have FW enabled generally, but during testing its handy to rule local FW out)
If there is a Firewall between client location & server location, have you tried setting an any<->any rule to avoid blocks there?

I also see Microsoft Oauth errors, which often relate to the certificates. Have you checked that all certificates are valid and clients are not prompted with certificate questions?

It might be an idea to log an incident with Microsoft if this is urgent under your partner agreement number. Looks like a few configurations might need to be verified.

Hi ,

Thanks for your suggestion, I have checked Availability service Error, that was generated for WSSecurity failed issue.
ProxyWebRequest FederatedCrossForest from user account to  from S-1-5-21-3298242413-1472053370-2507520255-778561 to https://outlook.office365.com:443/EWS/xxxxx.onmicrosoft.com/Exchange.asmx/WSSecurity failed
And the activsync warning is to increase the heartbeat interval.
How we can ensure that the issue is from Network end.

Thanks,
Dinesh

still some users are facing the issues, when they trying to open outlook, its keep on loading for 5 to 10 mins.

we have found out the root cause(DNS cache issue), thanks for the wonderful support.

Thanks for the update Dinesh, I am happy to see that the ExBpa suggestion seems to have potentially assisted in locating the bottleneck.
Good luck.