If the mail proxy being used by SEMS (Symantec Encryption Management Server) becomes unavailable, mail flow will be interrupted and the SEMS Mail Proxy settings will need to be updated. Using round robin DNS is not a viable solution to this problem.
The SEMS Mail log will contain error messages like this:
SMTP-00001: connection to mailserver.domain.dom[10.12.32.109]:25 failed: No route to host Mon Jul 29, 2013 at 12:49:48 PM +01:00
Each Mail Proxy entry in SEMS proxies to a single mail server. If that mail server is unavailable then SEMS will reject associated SMTP connections.
Symantec Encryption Management Server 3.3
PGP Universal Server 3.x