Define this relationship:
TableA::EmailField = TableB::EmailField
Go to a layout for TableA and add teh TableB::EmailField to the layout.
Enter find mode
Put a lone * in the TableB::EmailField
Perform the find.
Your found set will have all records in tableA that have a matching record in TableB.
Select SHow Omitted Only.
Your found set now has all those records in TableA that do not have a matching record in TableB.
This process can be scripted and you can use the omit option to reverse the results of the find from the start.