451 4.4.0 primary target IP address responded with “421 4.4.1 connection timed out” attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.
I solved this issue by adding many external DNS ip’s to the Hub transport what is the wrong with my DNS ?
I was using Domain Server DNS for all server’s ..
Now i faced problem with sending emails so i added World DNS IP’s Manually to the Hub Transport External DNS and changed from Ethernet DNS IP to hub transport External DNS