Check If use case is supported with Symantec DLP:
Symantec DLP Only (no CASB integration)
MIP label is not applied in OneDrive documents. Is this a supported use case with DLP Only without CASB?
Enforce and Endpoint Prevent: 15.8.x / 16.0.x /16.0.1.x / 16.0.2.x / 16.1
A Symantec DLP integration with Symantec CASB Cloud SOC would be required.
if a document is being created on user machine but being saved in OneDrive (instead of user machine), MIP Label will not be applied to that file. To apply MIP Label to this file, Securlet O365 is required (Symantec DLP integration with Cloud SOC CASB using Securlet O365 in CASB).