EmailMessage Restriction Rules

Hi Mark!

EmailMessage is a tricky one for access control because it contains potentially sensitive email content, and the standard object has historically had limitations around applying granular sharing controls. 

For now, I’d check whether the specific use case can be handled through existing sharing/access mechanisms or by controlling access to the related records. If the requirement is specifically to restrict individual EmailMessage records based on criteria, the Idea you linked is still the relevant place to track Salesforce’s progress. 

Hopefully Salesforce adds more granular restriction-rule support for EmailMessage in a future release.