I have 2 sites set up currently with a single Exchange 2013 Mailbox/Client Access server installed at each site (exch1 & exch2). The servers are members of a DAG (DAG1). exch1 is 2013 CU 6, exch2 is CU 5 (updating to 6 today). I have a third site going online shortly but right now is in its configuration stage just resides in a separate subnet in the same site exch1 resides in. I brought up a 3rd Exchange 2013 CU 6 server (exch3) and installed Mailbox/Client Access on it. This server is not a part of DAG1 and will just be relaying emails to sites 1 and 2. I have updated all receive connectors with exch3's ip to allow for mail connectivity. My issue is when I send an email from exch3, it queues up with delivery type 'SMTP Relay to Database Availibility Group' instead of making it to any of the other Exchange servers.
The specific queue error message is: 451 4.4.0 Primary Target IP address responded with "421 4.3.2 Services not available. Attempted failover to alternate host, but that did not succeed.
For brief moment during my testing I did get it to work but I restarted the frontend transport and transport service on exch3 to make sure everything was fine and it reverted back to hanging in the queue and has stayed this way for every configuration change I have tried to make since.
Any help would be gladly appreciated.