I was setting up two new Exchange 2013 servers with MBX/CAS roles and added them to the existing send connectors that route mail through a smart host. Apparently the guy who quit before I started never got the networking team to whitelist the IPs for these servers. Now, I've got a small chunk of mail sitting here that won't send because of this. My networking team says that they can't do anything about it until tomorrow night. I'm afraid that some business critical mail may have got caught before I noticed what was going on. My question is, how can I re-route the mail stuck in these queues to go out through the send connectors from the previously implemented Exchange servers?
First of all, you should remove these servers from the send connectors to avoid more messages being stuck. You can either remove them from GUI console or by using cmdlet Set-SendConnector
Check here for more details about Set-SendConnector
Secondly, you should export those messages stuck in queue as .eml files by using Export-Message cmdlet.
Check here for more details about how to use Export-Message
At last, you can put all these .eml files under Pickup or Replay folder on any working transport servers. The transport service will pick up all eml files there and submit them to re-transport.
Check here for more details about Pickup and Replay folder
Closely monitor the queue and ensure all emails are delivered, then you are good!