I have so far used the singular term, “e-mail server,” in describing the referral that began our investigation. It turns out to have been more complicated than that. Secretary Clinton used several different servers and administrators of those servers during her four years at the State Department, and used numerous mobile devices to view and send e-mail on that personal domain. As new servers and equipment were employed, older servers were taken out of service, stored, and decommissioned in various ways. Piecing all of that back together—to gain as full an understanding as possible of the ways in which personal e-mail was used for government work—has been a painstaking undertaking, requiring thousands of hours of effort.