I am running exchange server 2010 and I am noticing quite a few emails that will not leave the queue because of this error: 451 4.4.0 Primary target IP address with: "421 4.4.2 Connection dropped due to SocketError"
I have tried creating a new send connector to force helo but that didn't work.
I am able to telent from the exchange server to a problematic domain. I can also do a nslookup without issue from the exchange server to a problematic domain.
Everything I am reading says this a DNS issue but I can't find where or what needs to be added\changed.
We have not made any changes to exchange and it's not all domains but it does seem to be getting more and more.