As of July 2024, Cloudsoc Gatelet introduced the support to scan the payload of the predefined Google Apps which extends the scope to the Email Body of Gmail. This article goes into the steps to implement a policy around it.
Gmail Gatelet Enabled and fully functional
Email Body is a special type of object, as of 3.171 (July's version) which is presented differently by the SaaS App itself, different than File attachment or Messages.
1- Enabled the Payload Scan Feature on the tenant
2- Enable the 'Payload scan' on Gmail Gatelet
3- Build a DIM DLP policy
craft a policy around the use case to be covered, with the above configuration, the contents of the email would be sent to the DLP for inspection.
Here is a simple Keyword based policy:
This should match an email body like this: