App Sandbox
App Sandbox is a macOS security feature that restricts an application's access to system resources, files, and network connections, limiting the potential impact if the app or its dependencies have a vulnerability.
App Sandbox is a mandatory requirement for apps distributed through the Mac App Store. A sandboxed app runs in a restricted environment: it can only access files the user explicitly opens or selects (via Open dialogs or drag-and-drop), a temporary scratch directory, and a small set of system services. It cannot read arbitrary files from the filesystem, access other applications' data, or make unauthorized network connections.
The sandbox model means that even if a malicious MBOX file attempted to exploit a vulnerability in the parser, the damage it could cause is bounded by the sandbox's restrictions. The app cannot exfiltrate other files from the system, cannot write to arbitrary locations, and cannot communicate with external servers without explicit user permission.
Mbox Viewer operates entirely within the App Sandbox. It reads only the MBOX and EML files you open, writes only the companion index file in the same location (using sandbox-extended security-scoped bookmarks), and makes no network connections. The combination of sandbox enforcement and the app's local-only, read-only design provides strong privacy guarantees for your email archive.
Related terms
A macOS application bundle that contains native compiled code for both Apple Silicon (ARM64) and Intel (x86_64) architectures, running natively on either processor without emulation.
An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering.