Question/Issue:
When examining the SBG appliance messages queues, you see messages in the delivery queue with this listed as the message 421 4.4.0 [internal] "no MXs for this domain could be reached at this time."

Cause:
This is not an error but an description of why the message could not be delivered. The message indicates a general mail delivery attempt failure in which the appliance could not communicate with the remote mail system. This is usually the result of an inability to successfully connect to the remote host or to resolve the MX records or DNS host names for the email domain to which the appliance is attempting delivery.


Solution:
Possible circumstances that have been reported and cause this issue:

• The local MTA (SBG) cannot communicate with the remote MTA. Possible reasons for this are:
  1. Connection refused by remote MTA
  2. Connection times out while trying to connect to the remote MTA
  3. Mail Exchange (MX) record(s) and A records missing
  4. Firewall rule blocking connection from MTA IP address
• Destination management - Domain Settings
  1. Check Protocols > Domains
  2. Consider adding or modifying the Optional Destination Routing
• Masked mail banner - similar to the one found in Cisco Pix Mailguard/SMTP Fixup
• Issue with PTR or RDNS enforcement
• Invalid Response
• DNS query failure for calls larger than 512 bytes ( DNS UDP packet size has been limited to 512 bytes in SBG 8.0.2-12 and later )
  • Microsoft KB 828263: http://support.microsoft.com/kb/828263

Document ID: 2009032512563954
Last Modified: 08/05/2009
Date Created: 03/25/2009
Product(s): Brightmail Gateway
Release(s): BG 8.0