The debug logs for the SESC service show an error message similar to the following regarding a "silent ping" error similar to the following:
The default location for the SESC debug logs is C:\Program Files\Symantec\SESC\1.0\Logs\log.txt (for more details see the following article: How to Obtain Debug logs for Symantec Email Submission Client (SESC)).
The SESC service is unable to communicate with the Symantec ping server located at:
Ensure that the SESC computer has outbound access to port 80 to the Internet. If outbound access is not available this error message can be ignored.