When sending out external emails in HES, some emails are bounced back. You also receive a Non-delivery Receipt (NDR) message similar to this:
Diagnostic information for administrators:
Generating server: exchange-server.internal.domain.com
relay.sjc.mx.trendmicro.com #500 Firewall Error ##
The issue occurs because of incompatibilities or restrictions caused by the Cisco firewall configuration. The issue is more likely to occur if you are sending an email to multiple recipients or using a distribution list in Exchange 2007.
To resolve this, disable the ESMTP/SMTP inspection on the sender's firewall.
- On the router, run "show run" to identify the ESMTP/SMTP inspect rule.
- Disable the ESMTP/SMTP inspect entry in the Cisco firewall configuration by inserting the word "no" at the beginning of the line, as shown in the examples below:
- No ip inspect name TEST smtp
- No ip inspect name TEST esmtp