Could not resolve mail server name
because DNS server did not respond in time.
No inbound email even you can send emails
Can't past SMTP test because of modusGate or Vircom
Situations: 1. The client is running Exchange 2010 with Microsoft
failover cluster and there are two CAS servers. They can send email but
can't receive any outside email. The internal email works fine.
2. When outside people send an email to your email address, they may
receive this message: Could not resolve mail server name because DNS server
did not respond in time.
3. When you test SMTP using telnet, the prot 25 is open, but you can't
continue the rest test as shown below.
220 mai.chicagotech.net modusGate
ESMTP Receiver Version 5.1.1024.13396
250-X-IMS 5 -1
501 5.5.2 Syntax error in address email@example.com
Troubleshooting: 1. As said, telnet port 25OK.
2. nslookup shows correct MX record.
3. Finally, we found there are a lot email stay queue in
Vircom/modusGate and waiting for delivery. When we checked the Connection,
we found the Route IP for CAS is 10.0.5.220. We could not ping the IP adders
because the failover cluster broken last week and the failover doesn't work.
The temporary solution is modify the Routeon modusGate to ping to one CAS IP
only. After that, the queue emails released from the modusGate.
Contact a consultant