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Choose or drop a .mbox file. You can paste the contents instead.
MBOX Mailbox Viewer
Drop in an .mbox mailbox or paste its text and the viewer splits it into messages at each 'From ' separator line that follows an empty line, listing number, date, sender, subject and byte size. Type a number from the list into Open message number to read that one message: the sender's display name and real address are shown separately, along with To, Subject, Date, Message-ID and the envelope separator line. The body is shown as plain text, or, when only HTML exists, as HTML source that is never rendered. A headers table decodes RFC 2047 encoded subjects and names, and a MIME parts table lists each part's content type, charset, transfer encoding, attachment file name and decoded size. Scripts, event attributes and javascript: links in HTML are listed, and remote images and 1×1 tracking pixels appear only as host names and URLs with a load count of 0. The mboxrd or mboxo quoting format is assumed automatically or chosen by you, and the basis for that assumption is shown. A single message's raw source can be downloaded as .mbox when it is valid UTF-8 and within 100,000 characters.
File types: .mboxProcessing: This browser
or drop a file here
✓ Stays on this deviceMaximum size: 200 MB
How to use MBOX Mailbox Viewer
Let it read the file
The file is read and parsed in this browser — nothing is uploaded.
Check the result
Look over what came back, then copy it, download it, or move on.
Want to know how files are handled? Read the privacy notice →
Common questions
How do I open an MBOX file online without installing an email client?
Choose or drag the .mbox file onto this page and the full message list appears without any email client installed. Each row shows number, date, sender, subject and size. Type a row's number into Open message number to read that email's body, headers and MIME parts, or paste mailbox text instead of choosing a file.
How do I open a Thunderbird MBOX file in the browser?
Thunderbird keeps each folder as a plain mbox file with no extension, so copy that file, add .mbox to its name and open it here. The files sit in your profile folder under Mail or ImapMail and are named after the folder, such as Inbox or Sent; skip the matching .msf files, which are only indexes. A folder that has not been compacted can still hold messages you deleted, and they will show up in the list.
Is my MBOX file uploaded to a server when I view it here?
No, there is no upload: the MBOX file is read and parsed by the browser on your own device. The viewer does not send the mailbox or any message anywhere, does not fetch images referenced in emails, and does not save the file to browser storage, so closing the tab leaves nothing behind.
Can I view an MBOX file on an iPhone or Android phone?
Yes, open this page in Safari or Chrome on the phone and pick the .mbox file from Files or Downloads. The same 200 MB limit applies, but phones have less memory, so a mailbox close to that size may load slowly or make the browser reload the tab. Opening a message by number works exactly as on a computer.
Why is my MBOX file not opening with a 'not an MBOX mailbox' error?
That error means the first bytes of the file are not a 'From ' separator line, which every mbox mailbox must start with. Common causes are picking a PST, OST or single EML file, opening a still-zipped Takeout archive, or a blank line or other data before the first separator. Unzip it, check that the first line looks like 'From someone@example.com Mon Jan 1 00:00:00 2024', and try again.
Why does my MBOX list show fewer messages than expected or flag the last one as truncated?
Messages are split only at 'From ' lines that follow an empty line, and the list displays just the first 5,000 rows, so either can make the count look off. The Messages figure counts every message found, including those past row 5,000, which open by number. A last message without a final line break is flagged as possibly incomplete, usually after an interrupted export or copy. A Content-Length header claiming more bytes than exist is reported but never used for splitting.
What is the MBOX file size limit and how many messages can it handle?
The limit is 200 MB (209,715,200 bytes) per MBOX file and up to 1,000,000 messages; larger files are refused before anything is indexed. Within that, the list shows 5,000 rows, a message's body and raw-source previews stop at 100,000 characters, and one message may contain at most 2,000 MIME parts nested no deeper than 20 levels.
Do remote images and MBOX tracking pixels load when I open a message?
No, remote images, stylesheets and 1×1 tracking pixels are never loaded, so the sender cannot learn that you opened the email. They are listed in a Remote resources table with host, kind, URL and a load count of 0, which shows who the message would have contacted. HTML stays as source text; its scripts, event handlers and javascript: links are listed, not run.
Does a DKIM or SPF pass in an MBOX email header prove the sender is genuine?
No, the viewer shows DKIM, SPF and ARC results only as claims written into the message, and it checks none of them. Those headers can be forged or added after delivery, and this tool has no network access and no keys to verify signatures. The address and date in the 'From ' separator line are likewise only text written by the program that created the mailbox.
Can I convert an MBOX file to PST or EML with this viewer?
No, this is a read-only viewer and it does not convert a mailbox to PST, EML or PDF. What you can save is one message's exact raw source, separator line included, as a .mbox file, offered when that message is valid UTF-8 and no longer than 100,000 characters. Attachments are listed but cannot be extracted.
mboxrd vs mboxo: what is the difference in an MBOX file?
Both escape body lines starting with 'From ' by adding '>', but mboxrd can be undone exactly while mboxo cannot tell an added '>' from one that was already there. Automatic mode assumes mboxrd and shows the evidence, such as whether multi-level '>>From' lines exist. Choose mboxo to see the body with no '>' removed; any '>From' line is then flagged as not recoverable.
Which character sets can the MBOX viewer decode in email headers and bodies?
It decodes any charset your browser supports, including UTF-8, ISO-8859-1, Windows-1252, Shift_JIS, ISO-2022-JP, GBK and Big5, using the label each part declares. Decoding is strict, so wrong bytes give a visible charset error instead of guessed text. RFC 2047 encoded subjects, base64 and quoted-printable are handled; a text part with no charset is read as US-ASCII.