E5 license services to pick to ensure that email DLP will work correctly

Hi Afsar_Shariff 

Here is a link from Microsoft that I recommend saving, which highlights licensing requirements for Exchange DLP as well as many other security and compliance features.

https://learn.microsoft.com/en-us/office365/servicedescriptions/microsoft-365-service-descriptions/microsoft-365-tenantlevel-services-licensing-guidance/microsoft-365-security-compliance-licensing-guidance#microsoft-purview-data-loss-prevention-data-loss-prevention-dlp-for-exchange-online-sharepoint-online-and-onedrive-for-business

To answer your specific question, however, please make sure the "Exchange Online (Plan 2) feature is enabled if you have the E5 license.