Outlook still trying to connect to old exchange server after change all the dns record and settings to new server, after you make sure all the settings are correct ! have a look at ADSI Edit :
Connect to "Configuration" naming context, then Drill down to: CN=Services\ CN=Microsoft Exchange\ CN=<Your Org name>\ CN=Administrative Groups\ CN=Exchange Administrative Groups\ CN=Servers\ CN=<Your Server Name>\ CN=Protcols\ CN=Autodiscover\
delete the CN=<Your Server Name> of class serviceConnectionPoint in there
Good Luck