The security engine of Dynamics 365 requires that users have read access to Account records in order to use email templates regarding/related to Case records. This results in a situation whereby users who can access Case records only (but not Account records) are unable to use email templates on Cases.

Requiring access to Account records makes managing information security quite difficult. Granting access and sharing Account information with agents (who need not access Account information) just to enable them to use email templates on Cases compromises security, and is simply unnecessary.

Please consider revising the security engine to allow independent privileges to entities (tables).