Still outlook contacting old exchange 2010 server after miration to exchange 2013

Hi,

I have migrated ex2010 to ex13cu5, migration fine. But when I shutdown old exchange server outlook clients getting delay to update the folder. When I check on the connection status, it is trying to connect to old ex10 server (by fqdn then server name) then automatically close this query. Finally it will be fine!

If there is ex10 is online, no issue at all to connect and latency for updating folder.

Why it is still contacting old exchange server?

Autodiscover name , I set for all as below:

Set-ClientAccessServer –Identity CON-EX2010CAS - AutoDiscoverServiceInternalUri https://mail.contoso.com/Autodiscover/autodiscover.xml

Set-ClientAccessServer –Identity CON-EX2013CAS - AutoDiscoverServiceInternalUri https://mail.contoso.com/Autodiscover/autodiscover.xml

Thanks,