In Symantec Endpoint Protection (SEP), folder exceptions for mapped network drives do not work as you expect, and exhibit the following behavior:
\\server\share\folder1to X: does not respect exceptions for
This is partially fixed in SEP 12.1 RU6 MP4. Exclusions for the root of a mapped drive will work as expected in that version, but mapping drive letters to sub-folders of shares should still be avoided. All mapped drive exclusion issues were fully fixed in SEP 14.0.
Solution: upgrade to newest verision of SEP 12.1.x for partial fix, or upgrade to SEP 14.0 to resolve all mapped drive exclusion issues.
The full fix in SEP 14.0 should eventually be backported into SEP 12.1.x; this article will be updated as new information becomes available.