Free MBOX Viewer
Open a mailbox export from Gmail Takeout, Thunderbird or Apple Mail to list its messages, see who sends the most, and save the list as CSV.
What is a MBOX Viewer?
An mbox file stores a whole mailbox as one long text file, with each message starting on a line that begins with From and a space. Gmail Takeout, Thunderbird and Apple Mail all export this way, and this viewer turns one into a readable list.
It reads only the headers of each message, so even a large export lists quickly. Names and subjects are decoded, attachments are counted, Gmail’s labels are kept, and the list can be saved as CSV for a spreadsheet.
Key Features
Every Message Listed
Date, sender, subject and attachment count for each message, in the order they’re stored.
Top Senders
Messages counted per sender address and per domain, so you can see who fills the mailbox.
CSV Export
Save the list with dates, senders, recipients, subjects, attachments and Gmail labels for Excel or Sheets.
Decoded Headers
Encoded names and subjects, including Chinese, Arabic and emoji, are shown as text.
Your Mail Stays Here
The mailbox is read in your browser and never uploaded anywhere.
Perfect for everyone
- People moving off Gmail or Outlook
- Researchers and archivists working with mail exports
- Admins auditing a mailbox
How to Use the MBOX Viewer
Export the mailbox, open it here, and choose a view.
Export the Mailbox
Use Google Takeout for Gmail, or the ImportExportTools add-on or the folder file for Thunderbird.
Open the File
Choose Open .mbox file. Takeout names it after the label, such as All mail Including Spam and Trash.mbox.
Browse or Count
Messages lists everything, and Senders ranks addresses and domains.
Export to CSV
Switch to CSV and download it to sort and filter the list in a spreadsheet.
Mailboxes, Listed
Each row is a small mbox file and each answer is this viewer’s output in the mode on the chip. Count the messages before you reveal it.
“From 1781234567890123457@xxx Sun Oct 25 11:02:40 +0000 2026 X-Gmail-Labels: Inbox From: Grace Hopper <grace@example.net> To: ada@example.org Subject: Re: Notes on the engine Date: Sun, 25 Oct 2026 11:02:39 +0000 Looks good to me. From 1781234567890123458@xxx Sun Oct 25 12:30:00 +0000 2026 X-Gmail-Labels: Promotions From: Example Shop <news@shop.example.com> To: ada@example.org Subject: Autumn sale starts today Date: Sun, 25 Oct 2026 12:29:58 +0000 Up to 30% off mugs.”
“From - Sun Oct 25 09:14:02 2026 X-Mozilla-Status: 0001 From: Lin Wei <lin@example.cn> To: ada@example.org Subject: =?UTF-8?B?5Lya6K6u57qq6KaB?= Date: Sun, 25 Oct 2026 17:14:01 +0800 Minutes attached. From - Sun Oct 25 10:01:00 2026 X-Mozilla-Status: 0001 From: Lin Wei <lin@example.cn> To: ada@example.org Subject: Re: =?UTF-8?B?5Lya6K6u57qq6KaB?= Date: Sun, 25 Oct 2026 18:00:58 +0800 Corrected version.”
“From a Sun Oct 25 08:00:00 2026 From: Example Shop <news@shop.example.com> Subject: New arrivals x From b Sun Oct 25 09:00:00 2026 From: Example Shop <orders@shop.example.com> Subject: Order 1042 x From c Sun Oct 25 10:00:00 2026 From: Grace <grace@example.net> Subject: Lunch? x From d Sun Oct 25 11:00:00 2026 From: Example Shop <news@shop.example.com> Subject: Last chance x”
“From a Sun Oct 25 08:00:00 2026 From: Accounts <accounts@example.com> Subject: Invoices for October Date: Sun, 25 Oct 2026 08:00:00 +0000 Content-Type: multipart/mixed; boundary="b" --b Content-Type: text/plain Two invoices attached. --b Content-Type: application/pdf Content-Disposition: attachment; filename="inv-1.pdf" JVBERi0K --b Content-Type: application/pdf Content-Disposition: attachment; filename="inv-2.pdf" JVBERi0K --b--”
“From a@example.com Sun Oct 25 08:00:00 2026 From: Ada <ada@example.org> Subject: Meeting notes Date: Sun, 25 Oct 2026 08:00:00 +0000 Agreed points: >From now on we meet on Mondays. From here on, Bob takes notes.”
“From a Sun Oct 25 08:00:00 2026 From: "Lee, Sam" <sam@example.com> To: ada@example.org Subject: The "big" plan Date: Sun, 25 Oct 2026 08:00:00 +0000 Details inside.”
“From 1781234567890123457@xxx Sun Oct 25 11:02:40 +0000 2026 X-Gmail-Labels: Inbox From: Grace Hopper <grace@example.net> To: ada@example.org Subject: Re: Notes on the engine Date: Sun, 25 Oct 2026 11:02:39 +0000 Looks good to me. From 1781234567890123458@xxx Sun Oct 25 12:30:00 +0000 2026 X-Gmail-Labels: Promotions From: Example Shop <news@shop.example.com> To: ada@example.org Subject: Autumn sale starts today Date: Sun, 25 Oct 2026 12:29:58 +0000 Up to 30% off mugs.”
“From a Sun Oct 25 08:00:00 2026 From: Printer <scanner@office.example.com> Date: Sun, 25 Oct 2026 08:00:00 +0000 Scan attached.”
“From: Ada <ada@example.org> Subject: Just one message Pasted without the From separator line.”
“From a Sun Oct 25 08:00:00 2026 this line isn't a header nor is this one”
How an mbox File Is Built
mbox is simple, which is why it has lasted since the 1970s. These ten details explain how it holds a mailbox.
One File, Many Messages
Messages are stored back to back in a single text file, oldest first in most exports.
“How many files per mailbox?”
The From Line
Each message starts with From, a space, the sender and a date, on a line of its own.
“What follows From on that line?”
Then the Headers
After the From line comes the normal email: headers, a blank line, then the body.
“Is the From line part of the email?”
Quoting From in Bodies
A body line starting with From is written as >From, so it isn’t read as a new message.
“How is a body line “From here” stored?”
mboxo and mboxrd
mboxrd also quotes lines that already start with >From, so quoting can be undone exactly.
“Which variant can be undone exactly?”
mboxcl
Some systems add a Content-Length header instead of quoting, which other readers may ignore.
“Is Content-Length required?”
Attachments Inline
Attachments stay inside each message as Base64 MIME parts, which is why exports get large.
“Are attachments separate files?”
Gmail Labels
Takeout adds an X-Gmail-Labels header listing each message’s labels, such as Inbox or Important.
“Which header holds Gmail labels?”
Thunderbird Status
Thunderbird adds X-Mozilla-Status headers that record read and deleted flags.
“Does Thunderbird delete messages from the file right away?”
RFC 4155
The application/mbox media type was registered in 2005, describing the format as it’s used in practice.
“What media type does mbox use?”
Where mbox Files Come From
Most desktop mail apps and Google’s export tool write mbox, so a mailbox from almost anywhere except Outlook can be opened here.
Google Takeout
Choose Mail at takeout.google.com to get one .mbox per export, with labels in X-Gmail-Labels.
Thunderbird
Each local folder is an mbox file without an extension, inside the profile’s Mail folder.
Apple Mail
Mailbox, Export Mailbox writes a folder with an mbox file inside.
Linux Mail Servers
Traditional mail spools in /var/mail store each user’s mail as an mbox.
Not Outlook
Outlook uses .pst files instead. Convert them to mbox first, or open single messages as .msg.
mbox Pitfalls
What goes wrong with large mail exports, and how to get a file that opens cleanly here and in other tools.
Huge Takeout Files
A full Gmail export can be many gigabytes. Export a single label to get a file small enough to open.
Unquoted From Lines
Badly written files don’t quote From in bodies, which can split a message in two. This viewer requires a dated separator to avoid that.
Duplicate Messages
Takeout puts a message once even with several labels, but merging exports can duplicate it.
Line Endings
Files moved between Windows and Unix can mix line endings. They’re normalised when reading.
Encoding Problems
Old messages may lack charset information, so accented subjects can show as symbols.
Opening in a Text Editor
Large mbox files can freeze ordinary editors. Read the list here, then search the file with a tool built for big files.
When to Open an mbox File
Whenever a mailbox arrives as one file, from an export, a backup or a colleague, and you want to know what’s inside before doing anything else with it.
Leaving Gmail
Check what a Takeout export contains before deleting the account or importing it elsewhere.
Cleaning Up Subscriptions
Rank senders to find the newsletters and shops filling the mailbox.
Archives and Research
List an archived mailbox in a spreadsheet for review or analysis.
Legal and HR Requests
Produce a list of messages in a date range without importing the whole mailbox.
Checking a Backup
Confirm a backup holds the messages you expect before relying on it.
What the CSV Export Contains
The CSV has one row per message and a header row, quoted the way RFC 4180 asks, so Excel, Google Sheets and Numbers open it cleanly. These are its columns and how to use each one.
#
The message’s position in the file, starting at 1. Sort by it to get back to the original order after filtering.
Date
The Date header exactly as the sender’s client wrote it, with its time zone offset. Spreadsheets may need a formula to turn it into a real date.
From
The sender’s name and address as they appear in the header, decoded. Filter by domain to group mail from one company.
To
The recipients listed in the To header. Messages sent to a list or as a blind copy may show only the list address.
Subject
The decoded subject, with commas and quotes escaped so they stay in one cell.
Attachments
How many parts the message marks as attachments. Inline images in newsletters usually aren’t counted.
Gmail Labels
The X-Gmail-Labels value from a Takeout export, such as Inbox,Important. It’s empty for mailboxes from other apps.