I am trying to set up a cross site DAG to add site resilience to our Exchange 2013 system (all build 995.29).
I have 2 servers at the primary site (Exchange 1 and 2) both running CAS and DAG roles. All of the mailboxes are currently stored on Exchange1. Exchange1 is also the only server with an internet send connector and the one that our MX record points to.
I'm trying to set up the DAG between Exchange2(primary site) and Exchange3 which is located in a different subnet at a different site. The DAG will create ok and I can add both servers to it.
The problem occurs after the servers are added to the DAG. for some reason a fraction of the emails end up getting stuck in a mail loop on Exchange2 eventually they time out and a non delivery receipt is sent to the user.
I've had to roll back the changes now to allow full flow of email again but need to know why creating a dag can stop mailflow between two servers.
Thanks in Advance
