Parameter Value: [ID of an Account, Opportunity or other Salesforce object related via a WhatID]
Parameter Requirements: None
Parameter Description: EmailRelatedTo sets the value of the Related To field. This parameter now supports all WhatID objects in Salesforce. A list of supported objects can be found in the Salesforce article here: Object Reference for Salesforce and Lightning Platform.
The Related To field causes the sent email to appear in the Activity History related list of the object identified. EmailRelatedToId cannot be related back to a who ID (Lead or Contact ID)