People Smart finds people competently and relays messages to their email addresses so you can contact them.
In addition, People Smart can look up the person behind an email address in reverse email search.
With this, one can use an email address to find out the owners name and sometimes other identifiable information about them.
This search can be used to validate the identity of a sender or ensure you have the correct email address before sending out an email.
Since there isn't a single service responsible for creating all email addresses, there will likely never be a central email directory providing access to all of them.