All my mail stays in queue with the following error message:
<451 4.4.0 Primary target IP address responded with: "421 4.4.2 Connection dropped." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.>
Receiving mail is no problem.
Situation: exchange server [hub+mail role] , edge [edge role] both have Exchange SP1 installed.
Servers are both replying with "220" on port 25 so this is not a problem.