I can receive fine from all over the world, send messages internally but no luck sending externally to other domains.
I’m getting the 451 4.4.0 Primary target IP address responded with 421 4.2… unable to connect. For messages hanging in the queue.
On NSLOOKUP resolve distant domains fine, Server has a firewall rule allowing port 25, running Exchange diagnostics I do get ‘Remote server failed the mail acceptance test when trying to open the remote socket’, ‘remote socket not available’.
Install went fine with no issues, restarted Transport services several times, cleared the queue several times and resent messages only to see them hang.
Use MX record is checked, use ‘external dns’ is checked, etc.
So where do I look at next?