Online Mbox Viewer

Read .mbox email archives online — free, private, and 100% in your browser. Your file is never uploaded.

🌐 onlinemboxviewer.com

English · Español · Deutsch · Français · Português (BR) · 日本語 · Italiano · Nederlands · 한국어 · Polski

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Why this project exists

A .mbox file is a whole mailbox squeezed into a single file — the format you get from a Google Takeout export, Apple Mail, or Thunderbird. Opening one usually means installing a desktop email client and importing it.

Online Mbox Viewer skips all of that: drop the file on the page and read it. The catch most "online" tools have is that they upload your email to a server. This one doesn't — the entire viewer runs as JavaScript in your browser, so your messages never leave your device.

Features

• 100% client-side — the .mbox file is parsed in memory on your computer. No upload, no backend, no account.
• Safe rendering — message HTML is sanitized with DOMPurify and shown inside a sandboxed <iframe> with a strict Content Security Policy.
• No tracking pixels — remote images are blocked by default; you can load them per message. Inline images are embedded locally.
• Gmail-aware — reads X-Gmail-Labels and lets you filter the message list by label. Attachments are downloadable.
• Multilingual & SEO-ready — 10 languages with localized URLs, hreflang, sitemap and structured data.
• Fast & static — built with Astro, deployed on Cloudflare Pages.

Also: Mbox Viewer for Mac

The online viewer is tuned for files up to 25 MB. For full Gmail Takeout exports, full-text search, folders and export, there is a native desktop app — Mbox Viewer for Mac (Windows coming soon).

Related projects

• mboxShell — the open-source terminal (CLI/TUI) tool to read, search and export .mbox archives. It's the sibling project and a direct source of inspiration for this viewer.
• Mbox Viewer — the native desktop app for Mac (Windows coming soon), for archives of any size.

Tech stack

• Astro 5 (static output) + TypeScript
• Tailwind CSS 4
• postal-mime for MIME parsing, DOMPurify for sanitization
• Hosted on Cloudflare Pages

Development

pnpm install      # or npm install
pnpm dev          # start the dev server at http://localhost:4321
pnpm build        # build the static site to dist/
pnpm preview      # preview the production build

Node 22+ is recommended (see .node-version).

Deploy (Cloudflare Pages)

• Build command: pnpm build
• Build output directory: dist

The build also generates dist/_redirects (301s from English slugs under a language prefix to the localized slug) and dist/sitemap-index.xml.

Project structure

src/
├── components/        UI + page components (Header, Footer, viewer, etc.)
├── data/              content in data files (viewer copy, FAQ, compare, legal…)
├── i18n/              locales, localized routes, UI strings
├── layouts/           BaseLayout (SEO, hreflang, Open Graph, analytics)
├── pages/             routes (English at root, /[locale]/ for the rest)
├── scripts/           mbox-viewer.ts — the client-side viewer engine
└── styles/            global.css (design tokens)

License

MIT — Copyright (c) 2026 David Carrero Fernández-Baillo — https://carrero.es

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Part of the mbox family of open tools, alongside mboxShell (terminal) — the related project and source of inspiration — and Mbox Viewer (desktop). Built by David Carrero Fernández-Baillo.