MBOX Viewer Online: Read MBOX Email in Your Browser, No Install

It reads the file in 4 MB chunks in a background worker and keeps only a small index in memory. The index records where each message starts, plus its subject, sender and date. A message is parsed when you click it, so a mailbox up to 2 GB fits in the browser.

Type part of a subject or sender name to narrow the list as you type. A counter above the list shows how many messages match. The filter checks subject and sender only, not message text or dates, and keeps the file's order.

HTML mail keeps its formatting. Plain-text emails appear in a monospace block. Embedded pictures (cid links) display without a network request. Encoded headers, such as a Cyrillic sender name or Café in a subject, are decoded to normal text.

Each attachment appears under the message with its size and a Download button. This free MBOX viewer does not preview files inside the page. Save the attachment and open it in its own program.

Each message is cleaned by DOMPurify and shown in a sandboxed frame where scripts are blocked. Links open in a new tab, and javascript: links are stripped out.

Thunderbird, Google Takeout and Apple Mail write the 'From ' separator line differently, and the viewer handles all three. A body line such as 'From the desk of...' does not split an email, and both LF and CRLF line endings work. If a file uses odd separators, a notice warns that a few may be split or merged.