What are the domains? Could be bad bounces from spam to non-existent domains Your server can not contact them, so it tried alternates either in dns or per the RFC’s (for example A record of domain.com) and that failed. So it is still trying.
Do an MX lookup from your transport server to verify your DNS is working. Then try telnet port 25 from the transport server to that IP to verify connectivity. What do you get? From: [email protected] [mailto:[email protected]] On Behalf Of Steve Ens Sent: Tuesday, October 7, 2014 3:42 PM To: [email protected] Subject: [Exchange] 421 4.2.1 Unable to connect errors Odd errors in my mail queue. Just started appearing yesterday. Most mail gets sent, but from certain domains I get these errors. "Attempted failover to alternate host, but that did not suceed." Anyone see this before? Exchange 2010 on Windows 2008 R2.
