I have two separate physical sites, Site A and Site B. In site A, I have following:

• 2 CAS servers
• 2 Hub Transport servers
• 2 Mailbox servers
• 2 Edge servers

In site B, I have the following:

• 1 CAS
• 1 Hub
• 1 Mailbox
• 1 Edge

Currently everything is working out of site A. That is, all users are housed on mailboxes that are in site A and all inbound mail flow is pointing to site A. I would eventually like to be able to move some of the mailboxes to site B without causing a disruption for resliency and redundancy purposes but I am not quite sure how to go about setting this up or if it is even possible.

So far I have created an Edge subscription in site B and am able to send emails out from test accounts set up with mailboxes on the site B Mailbox server. However, I am unable to receive incoming mail messages and am confused.

So I'm thinking incoming mail messages are still being directed to site A and then they are getting stuck because there is no way to route the mail to the site B mailboxes. Is this assumption correct? I am unfamiliar with mail flow and routing so I am not really sure what I need to be looking at?

Would I add the site B hub transport to the Edge subscription in site A? Or I guess more specifically, how would I go about enabling communication and mail flow between mailboxes split up on site A and B?