If Encryption Management Server is configured to proxy both inbound and outbound email to an MTA such as Symantec Messaging Gateway or Cisco IronPort which routes email based on rules, some email messages may get caught in a loop. For example:
Symantec Encryption Management Server 3.4.2 and above.
Rather than relying solely on, for example, message attachment names, create a rule in Encryption Management Server to add a unique X-Header to each message that is processed.
The MTA will be able to use the presence of the X-Header in its rules to determine whether Encryption Management Server has processed the message.
Note that by default, this X-Header is added to every message that Encryption Management Server processes:
However, if a third party uses Encryption Management Server, email sent from them will also contain that X-Header so it cannot be relied on by itself under all circumstances.
To add a unique X-Header, do this from the Encryption Management Server administration console:
By adding the new rule to the Default policy chain, the X-Header will be added to both inbound and outbound messages. An alternative would be to add different X-Headers to the Outbound and Inbound policy chains.