Why are CRM Approved Email Sent email records created without stamping a Sent Date or Account?
If there is no Sent Date or Account populated on a Sent Email record it could be that the Sent Email record is what is called a Sent Email Stub record.
A Sent Email Stub is created by the Integration User when a Sent Email record is created with Activity Tracking Mode set to Anonymous. The Sent Email Stub record is utilized by the system to associate Email Activity independent of the Account to maintain anonymity.
An easy way to identify whether a Sent Email record is a Sent Email Stub or not is to look if the VExternal_Id_vod__c field is populated on the Sent Email record. If there is a value populated in VExternal_Id_vod__c and the Account field is blank the record is a Sent Email Stub record.
CRM Help Documentation: