Which of the following methods blocks users from conducting mass data exfiltration using external devices?

Removable/External Media Blocking is a method specifically designed to prevent users from transferring data to external devices, such as USB drives or external hard drives. By implementing this control, organizations can significantly limit the risk of mass data exfiltration, which refers to unauthorized transfer of sensitive information outside of the organization's network. This control works by either disabling the use of these external devices altogether or by restricting access to them based on user roles, thereby ensuring that sensitive data cannot be easily removed from the organization's premises.

The other methods mentioned, while important for overall data security, do not specifically focus on blocking the use of external devices for data transfer. Data encryption protects the confidentiality of the data itself but does not prevent its movement; access control regulates who can access certain data but does not directly restrict data transfer methods; and network segmentation is effective in controlling network traffic and limiting exposure but does not inherently prevent users from using external devices for data exfiltration. Thus, Removable/External Media Blocking directly addresses the issue of preventing unauthorized data transfers to external media, making it the correct choice for this scenario.