Integrated email and contact database.
This system employs the simple act of soliciting the contact details of people you are already in email contact with.
Assuming that most people you are emailing are engaged in some kind consensual communication with you, they are more likely to accept the automatic invitation to submit contact details.
How it works -
All email messages sent via Irational webmail is designed with a signature file that requests a submission or update of personal contact details. If the reciever chooses to update their contact details they can click on the highlighted URL in the body of the email message that takes them to a database entry form where they can type in the relevant information. The data is stored in an online searchable contacts database that is accessible by any Irational member with the required password.