Explanation/Reference:
Explanation:
Exchange Server 2013 CAS role proxies the OAB download request to a "nearest" mailbox server hosting an active Organization Mailbox.
Both London and New York host a mailbox server and a client access server.
Therefore, you need to create a new active Organization Mailbox
Administrators can create additional Organization Mailboxes for fault tolerance or for serving users in a geographically disbursed Exchange deployment.
The Organization Mailbox
The Organization Mailbox is a new type of arbitration mailbox introduced with Exchange 2013.
The arbitration mailbox with persisted capability OrganizationCapabilityOABGen is referred to as Organization Mailbox. It plays a crucial role in OAB generation, storage and distribution.
Each Exchange Server 2013 mailbox role hosting an Organization Mailbox will generate all Exchange
2013 OAB's defined in the environment. The OAB is generated in the Organization Mailbox first and later copied to the disk.