In the patron import tool, the "Field to use for record matching" setting only offers options for the card number, username and those patron attributes marked as "unique identifier". It would be useful to have the email field as a matchpoint. For library teams in a health or academic setting especially, the email address will often be the unique ID that allows a check on whether the user is already in the system.
This would be highly useful for us in the UK health sector, as we rely on the email address to identify duplicate users. On importing member records we have found this causes many duplicates, as we are unable to select this option to identify duplicates.