Which of the following is used to provide secure file storage to network users only?

A NAS device is a purpose-built appliance that attaches to a local area network and exposes shared storage to authorized network users via file-sharing protocols such as SMB/CIFS or NFS. Unlike direct-attached storage, its design inherently restricts access to network-connected users, making it the correct answer for secure, network-only file storage.

IMAP (Internet Message Access Protocol) is an email retrieval protocol used to access mailboxes on a mail server; it does not provide general file storage.

A SAN (Storage Area Network) provides block-level storage typically accessed by servers rather than individual end users, and it is not used for general user file storage in the way NAS is.

SSH (Secure Shell) is a network protocol used for secure remote command-line access and encrypted file transfer (via SCP/SFTP), not a storage solution.