MBOX Viewer

Google Takeout hands you your Gmail as an .mbox file, and then leaves you alone with it: no Google tool opens it, and the standard advice is "install Thunderbird and import your entire mail history into it," which is a lot of ceremony to read some emails. The other advice - an upload-based mbox viewer - is worse, because a mail archive is the single most private file you own. This page is the quiet third option: mbox is just messages concatenated with From  separator lines, so the viewer indexes those boundaries in your browser, lists every message, and decodes one only when you click it.

The reader is the same engine as our MSG / EML viewer: multipart bodies, encoded subjects, quoted-printable and base64, attachments downloadable from memory, HTML rendered in a sandboxed frame with scripts stripped and remote tracking images blocked. Browsing stays fast in big boxes because nothing is decoded until you ask.

How to use the MBOX viewer

1. Click Choose an .mbox file, or drag the file onto the drop area.
2. Wait for the status line to say how many messages were indexed.
3. Scan the message list. Each row shows the sender, the subject, and the date. The list holds the first 400 messages in file order.
4. Click a row to open that message. The header card shows From, To, Cc, and Date, attachments appear as buttons you can click to save, and the body renders in the frame below.

How the mbox format marks where messages begin

An mbox file is many email messages stored one after another in a single text file. Each message starts with a separator line that begins with the five characters From (the word From followed by a space). This line comes before the message's own headers and is not part of the message. Traditionally it holds the envelope sender and a date, for example From alice@example.com Tue Sep 15 09:00:00 2026. Gmail Takeout writes an ID in place of the address.

That design has one weak point: a body line that happens to start with "From " looks exactly like a separator. Mail programs deal with it by quoting such lines with a >. Several variants grew up around this. In mboxo, only lines starting with "From " are quoted, so the change cannot be reliably undone. mboxrd also adds a > to lines that already start with >From , which makes it reversible. There is no field that says which variant a file uses, and no declared character set.

The viewer treats any line that starts with "From " at the beginning of the file or right after a line break as a new message. When you open a message, it removes that first line, turns >From back into From , and decodes the rest as a normal email, applying the character set each MIME part declares.

Worked example

From 1790000000@xxx Tue Sep 15 09:00:00 +0000 2026
From: Alice Grant <alice@example.com>
Subject: Shipping schedule
Date: Tue, 15 Sep 2026 09:00:00 +0000

We ship on Fridays now.
>From the archive: the old schedule is attached.

From 1790000001@xxx Tue Sep 15 10:00:00 +0000 2026
From: Ben Ito <ben@example.com>
Subject: Re: Shipping schedule
...

The viewer indexes two messages. The list shows "Alice Grant" with the subject "Shipping schedule", and "Ben Ito" with "Re: Shipping schedule", each with its date in your local format. Opening the first message shows the quoted line as "From the archive: the old schedule is attached."

Common problems and fixes

• A message stops mid-sentence and the next row says "(no subject)". Cause: the program that wrote the file did not quote a body line starting with "From ", so the viewer split the message there. Fix: open the next row, which holds the rest of the text.
• The status says the list shows only the first 400. Cause: the list is capped at 400 rows, and later messages cannot be opened from it. Fix: export a smaller archive. Google Takeout lets you pick individual Gmail labels instead of all mail.
• An Apple Mail export will not open. Cause: Apple Mail exports a folder named Something.mbox, and macOS displays it as a single item. The actual mailbox is a file named mbox inside it. Fix: right-click the folder, choose Show Package Contents, and open the file called mbox.
• Sender names show characters like "José". Cause: the header contains raw UTF-8 bytes rather than encoded words, and the viewer reads headers as Latin-1. Bodies are unaffected because they carry a charset. Fix: the address in angle brackets is still correct, so rely on that.
• A date is missing in the list. Cause: the message has no Date header, or the browser cannot parse the one it has. Fix: open the message and check the separator line's date in a text editor.

Related tools

For a single saved message, use the MSG / EML viewer. To pull contacts out of a phone or address book export, use the VCF to CSV converter.

Questions this tool gets asked

How do I open an .mbox file without Thunderbird?

Drop it on this page. The mbox format is a plain concatenation of email messages, and this viewer indexes it in your browser - a message list with sender, subject, and date, and a full reader for each message including attachments. No mail client, no import, no upload.

Can it open a Gmail Takeout export?

Yes - Google Takeout delivers your Gmail as .mbox, and that is exactly what this page reads. A whole mail archive is about as private as files get, so the fact that it never leaves your machine is the point.

Is my mail archive uploaded?

No - never. The file is indexed and read entirely by JavaScript in your tab. There is no upload endpoint on this site. Load the page, go offline, and it still works.

How large a file can it handle?

The whole file is held in your browser's memory, so a few hundred megabytes is comfortable on a normal machine; multi-gigabyte archives depend on your RAM. Messages are only decoded when you open them, which keeps browsing fast even in big boxes. If your archive is too big, split it by year in Takeout.

Are remote images and scripts blocked?

Yes - message bodies render in a sandboxed frame with scripts stripped and remote images blocked, so newsletter tracking pixels stay dead. Images embedded in the message itself are shown.

Can't I just open an mbox file in a text editor?

Technically yes - mbox is a 1970s plain-text format, messages stacked end to end with From separator lines. Practically no: a Takeout export is thousands of messages with base64-encoded bodies and attachments inlined as text walls, and editors choke on the file size. This viewer reads the same plain text, but with an index, decoding, and a message list - and Thunderbird's known slowdown on multi-gigabyte imports never enters the picture.

Related tools

• msg / eml → readable emailOpen Outlook emails - body, headers, attachments - without Outlook.
• ics → readable eventsOpen calendar files - events, attendees, locations - and export CSV.
• vcf → csvContacts out of vCard files and into a spreadsheet, locally.
• base64 ⇄ textBase64 both directions, UTF-8 safe, emoji included.