Hello,
SEP 12.1 is designed to communicate with certain Internet URLs to validate licenses, submit samples of suspicious files and use the new file reputation security features. If a proxy or corporate firewall blocks access to these URLs, then errors will result.
Insight: URL that SEP clients send reputation requests to. https://ent-shasta-rrs.symantec.com
Check this Article:
Required exclusions for proxy servers to allow Symantec Endpoint Protection to connect to Symantec reputation and licensing servers
http://www.symantec.com/docs/TECH162286
Expected behavior of Download Insight http://www.symantec.com/docs/TECH171776
How Symantec Endpoint Protection uses reputation data to make decisions about files
http://www.symantec.com/docs/HOWTO55275
VIDEO:
Symantec Download Insight in Symantec Endpoint Protection 12.1
https://www-secure.symantec.com/connect/videos/symantec-download-insight-symantec-endpoint-protection-121
Secondly, Download Insight has the following dependencies:
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Auto-Protect must be enabled
If you disable Auto-Protect, Download Insight cannot function even if Download Insight is enabled.
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Insight lookups must be enabled
Symantec recommends that you keep the Insight lookups option enabled. If you disable the option, you disable Download Insight completely.
Note: If Download Protection is not installed, Download Insight runs on the client at level 1. Any level that you set in the policy is not applied. The user also cannot adjust the sensitivity level.\
Even if you disable Download Insight, the Automatically trust any file downloaded from an intranet website option continues to function for Insight Lookup.
Reference: How Symantec Endpoint Protection protection features work together
http://www.symantec.com/docs/HOWTO55268
Hope that helps!!