Which feature does Exchange Server use to manage user mailboxes?

The feature that Exchange Server uses to manage user mailboxes is the mailbox databases. Mailbox databases are fundamental components within Exchange that store user mailboxes and their associated information, such as emails, calendar items, and contact details. These databases facilitate various operations, including the creation, retrieval, and management of mailbox content.

By using mailbox databases, Exchange can efficiently organize and manage large volumes of user data, ensuring that users have reliable access to their email and other mailbox contents. This structure allows for backup and recovery processes, scaling, and performance optimizations tailored specifically for user mailbox data.

Other options, while relevant to the overall functioning of email systems, do not directly manage user mailboxes. For instance, mail routing protocols pertain to how messages are directed through email systems; user management logs deal with tracking interactions with user accounts, and message queues relate to the temporary storage of email messages during transmission. None of these elements serve the primary function of managing user mailboxes as directly as mailbox databases do.