When looking for duplicate Contacts or Leads you may want to run a scenario based on just email address (ideally this would be a later pass after previously identifying dupes with fields in addition to email, e.g. first name, last name, phone etc.).
This will of course identify additional dupes that may have not been found in previous passes, but in addition you may be surprised to find instances where the email address DOES NOT MATCH the name fields at all!
This can happen when a user "clones" an existing Lead or Contact and updates the new data for this record, but leaves the old email address (probably doesn’t have the email for this new person).
Now that you have identified these in the Single Table Dedupe, just right click on the email address of the records that are incorrect, select "update value", and blank out the email field.