This error indicates the connection died after the we sent the data, often a sign that the receiving server's content filtering is being maxed out or that there is some type of connection filtering on the server/firewall.
For our customers using Cisco PIX or ASA firewalls, we suggest that the SMTP Fix Up or Inspect ESMTP settings be disabled on your firewall.
These settings have been known to be related to undelivered or delayed inbound and outbound messages. For additional information regarding this issue, please see:
For information on these settings and how to make changes, please see the links below:
3rd Party Blog - Cisco ASA Disable ESMTP Inspection:http://www.petenetlive.com/KB/Article/0000536.htm
Cisco Security Appliance (PIX 500 series, ASA 5500 series) Inspect Command Reference:http://www.cisco.com/en/US/docs/security/asa/asa72/command/reference/i2_72.html#wp1670771
Cisco PIX 6.3 Configuring Application Inspection (Fixup):http://www.cisco.com/en/US/docs/security/pix/pix63/configuration/guide/fixup.html#wp1103488
Cisco Catalyst 6500 Series Switch and 7600 Series Router Firewall - Configuring Application and Protocol Inspection:http://www.cisco.com/en/US/docs/security/fwsm/fwsm22/configuration/guide/fixup.html#wp1103488
Microsoft TechNet - You Cannot Send or Receive E-Mail Messages Behind a Cisco PIX Firewall:http://technet.microsoft.com/en-us/library/dd277550%28v=exchg.80%29.aspx
Please note that making any configuration changes to your networking appliances can have wide-reaching consequences. Please consult your organization's change control procedures before altering any settings.