Got two active directory sites with two exchange 2010 servers one in each site. Each server having CAS,hub and mailbox roles.
Two send conenctors have been created one at each site to send extranl email.At the site A evry now and then emails are struck int he queue with the message "451 4.4.0 primary target IP address responded with 421 4.4.2 connection dropped due to connectionreset attempted failove to alternate host but that didnot succeed".
Don't need to do any thing it does clear up it self once logged onto the server.
It happens to all the domains.
we are using Cisco ASA 5520 and disbled ESMTP.
Enabled SMTP verbose logging and didn't help much.
Send connector are using DNS and no smart hosts.
TCP offloading has been disabled on the exchange server