Obtaining the primary Email address of any Facebook user

Given only their ID, it was possible to obtain the primary email address of any Facebook user regardless of their privacy settings.

Anyone who has subscribed to a public mailing list knows the problem of members inviting their entire contacts list, including the mailing list, to every new social site and app. This has turned mailing list archives into a Wayback Machine for email notifications. Searching through some old mailing lists I came across a Facebook invitation reminder circa 2010:

Facebook

Obtaining the primary Email address of any Facebook user | Stephen Sclafani blog