Salesforce Fact #659 | RelatedToId on EmailMessage object
The RelatedToId field on EmailMessage object represents nonhuman objects such as Accounts, Opportunities, Campaigns etc. So, whenever we send out an email from a lead or contact record page, new row gets created but the RelatedToId field is blank for that record. Reference: https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/sforce_api_objects_emailmessage.htm Attached is the screenshot.