Server A running Windows Server 2008 acting as the DC. Server B running Windows Server 2008 running Exchange Server 2010.
When creating a new user account on Server A, the new user does not appear under New Mailbox - Add User under Exchange Management Console until about 10 minutes later. But it does appear under Active Directory Users and Computers on Server B immediately.
If a new user account is created using Exchange Management Console, it takes about 10 minutes before the new account shows up under Active Directory Users and Computers on either server.
It appears there is a delay somewhere, but where?