.mbox Viewer Online

How to open an MBOX file

1. Drop the .mbox file onto the box above, or click to choose it. Thunderbird’s mailbox files have no extension (they are just called Inbox, Sent and so on) and work the same way.
2. The file is indexed and the message list fills in. Search by subject or sender, or sort by date.
3. Click a message to read it. Download its attachments, or save that one message as an .eml file.

What an MBOX file is

An mbox file is a whole mail folder stored as one long text file: every message in full, one after another, each introduced by a line that starts with From . It is the oldest mailbox format still in everyday use. Google Takeout hands you your Gmail as a single file, usually named All mail Including Spam and Trash.mbox. Thunderbird stores each folder as an mbox file inside your profile. Many backup and migration tools write it too.

The catch is that nothing opens it by double-clicking. You are expected to import it into a mail program, which for a Takeout archive means installing Thunderbird and waiting while it copies years of mail, just to find one message.

Built for large mailboxes

The file is never loaded into memory. It is read from your disk in slices to find where each message starts, and only the message you click is read in full. In testing, a 2.4 GB mailbox with 600,000 messages was indexed in about four seconds, and messages past the 2 GB mark opened normally. The list stays responsive because only the rows on screen are drawn.

Details that matter

• Gmail labels from Takeout are shown next to each message and are included in search.
• Body lines that begin with “From” are stored escaped as >From in mbox files. They are restored when a message is opened, so text and saved .eml files match the original.
• Search looks at subject, sender and labels. It does not search inside message bodies.
• Messages are found by their From separator lines. Mailbox variants that rely only on a Content-Length header to separate messages are not supported.

Privacy

A mailbox export is your entire correspondence. Uploading it to a website to “view” it would hand all of it over. Here the file stays on your disk and is read by your browser; nothing is sent to a server. Remote images inside messages are blocked, so browsing old newsletters does not ping their senders.

Frequently asked questions

How do I open the .mbox file from Google Takeout?

Unzip the Takeout archive, find the .mbox file in the Mail folder and drop it on this page. It is indexed in your browser and shown as a searchable list of messages.

Can it open a very large MBOX file?

Yes. The file is read in slices and never loaded into memory. A 2.4 GB mailbox with 600,000 messages was indexed in about four seconds in testing.

Can I save one message out of the mailbox?

Yes. Open the message and choose “Save message as .eml”. You get that message exactly as it is stored in the mailbox, ready to open in any mail program. Attachments can be downloaded separately.

Does it work with Thunderbird mailbox files?

Yes. Thunderbird folder files such as Inbox or Sent, which have no file extension, are recognised by their content and opened as mailboxes.

Is my mailbox uploaded?

No. The mailbox is read from your disk by your browser. Nothing leaves your device.