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Univik Online MBOX Viewer
100% private. Runs only on your device
The per folder .mbox files that Proton Mail Bridge and a mail client produce, or the .eml files from the Proton Export Tool. Read on any device, decrypted mail kept on it.
Or pick it from your device. Messages open in this tab, on your own computer, phone or tablet. Your mailbox is never uploaded.
Proton, still ProtonMail to many of its users, encrypts your mailbox end to end. Nothing can read it without a key to decrypt it, and an export is the one moment that mail sits on your disk in the clear. This page opens that export in your browser on the same machine and sends nothing anywhere. The privacy you chose Proton for does not end at the export step.
Decrypted mail is exactly the thing you do not want on someone else's server. The tool reads the file locally and makes no copy of it.
Bridge exports through a client give you a separate mailbox file for Inbox, Sent, Archive and each label folder. Open them one by one or the whole export folder together.
The Proton Mail Export Tool writes each message as its own .eml beside a JSON file. Drop an .eml here and it opens as a one message mailbox.
Bridge needs Thunderbird, Apple Mail or Outlook to make the export. Reading it afterwards needs none of them.
Short answer: the export is plain mbox once Bridge and a client have written it. Copy it to any device you trust, open this page and pick the file.
Bridge runs on Windows, so the export is usually made here. Read it in Edge, Chrome or Firefox without opening Thunderbird again.
If Apple Mail wrote the export through Bridge, you have a .mbox package. Use Select a folder on it here in Safari or Chrome.
Bridge ships for Linux as well, and a Thunderbird export lands as an ordinary mbox. Open it in Firefox or Chromium on the same box.
The Proton app on iPhone or Android reads the live account, not an export. Move the mbox to the phone over a cable or a private share and read it here in the browser.
No Bridge on ChromeOS, but an export made elsewhere opens here in Chrome from Files or a USB stick.
Proton has offered three different ways out over the years, and they do not all produce the same files. The tool copes with each.
ImportExportTools NG exports a folder, with subfolders if you like, as mbox. Those files are standard mboxrd and open here with every message and attachment.
Export Mailbox in the Mail app writes a .mbox package for each Proton folder. Pick the package with Select a folder and the tool finds the mailbox inside.
Proton's old desktop app wrote one .mbox per folder before it was discontinued. Exports made with it years ago still open here unchanged.
The current Export Tool saves one .eml per message plus a JSON file of metadata into a folder named after the account and the date. Each .eml opens here on its own; the JSON is for Proton's restore.
Message-ID, Received and DKIM lines from before Proton encrypted the message are shown as stored, useful when you need to trace where something came from.
Attachments open from their own tab, singly or as a zip. HTML mail renders with inline pictures while remote images stay blocked.
On a paid plan run Proton Mail Bridge, add the account to Thunderbird and export a folder as mbox with ImportExportTools NG. Apple Mail users can use Export Mailbox instead.
Drop the .mbox onto the box at the top, or use Select a folder on the export directory to open every folder at once.
Open a message and look at the Headers and Attachments tabs. Save anything as .eml or a zip. The export is never written to.
Proton's own documentation describes these routes. Which one you used decides what files you have.
Available on paid plans such as Mail Plus and Proton Unlimited. It runs a local IMAP and SMTP server, decrypts on your device and lets Thunderbird, Apple Mail or Outlook download the account. The client's own export then writes mbox.
Free for every account. A command line backup tool, proton-mail-export-cli, that saves the whole mailbox as .eml and .json files under you@proton.me/mail_YYYYMMDD_HHMMSS/. It restores only its own backups.
Discontinued between late 2023 and early 2024. It exported folders as .mbox or .eml in bulk. If you still have those files, they are ordinary mbox and open here.
Proton has both. Through Bridge, folders appear as IMAP folders and labels appear under a Labels tree, so a full export can give you an mbox per label as well as per folder.
Easy Switch pulls mail from Gmail, Outlook or IMAP into Proton online. To import local .mbox or .eml files you need Bridge and a client that can import them.
This online page reads one Proton export wherever you are without installing anything. For a folder of per label exports opened together, search inside message bodies and printing, the free Univik MBOX Viewer for Windows is the one to install.
| Feature | Online Proton Viewer | MBOX Viewer for Windows |
|---|---|---|
| Install needed | None, opens in the browser | 15 MB Windows setup |
| Operating system | Windows, Mac, Linux, Chromebook, iOS, Android | Windows 7 to 11 |
| Files uploaded | Never, runs on your device | Never, runs on your PC |
| Per folder exports | One export folder at a time | Whole export tree at once |
| Search | Sender, subject, recipients | Message bodies too |
| Large mailboxes | Read in pieces, multi GB files open | No size limit |
| Browser print of the open message | Direct printing | |
| Price | Free | Free |
Yes, through Proton Mail Bridge and a desktop client. Bridge, on a paid plan, lets Thunderbird or Apple Mail download the account. Their export functions then write mbox. The free Proton Mail Export Tool writes .eml and .json instead. Both kinds of file open on this page.
Yes. Each .eml is a single complete message, and the tool treats it as a mailbox with one entry. Pick several at once and switch between them from the top bar. The .json files beside them hold metadata for Proton's restore feature and are not needed for reading.
Online here means the viewer arrives as a web page, not that your mail goes anywhere. Your browser opens the file from local disk, there is no server on the other end and no account. Take the machine offline once the page is up and it keeps reading, which proves the point.
That is how mbox works: one file holds one folder. Thunderbird's export and the old Import-Export app both wrote Inbox, Sent, Archive and each label as its own file. Put them in one folder and use Select a folder here to load them all together.
For Bridge, yes: it comes with Mail Plus, Proton Unlimited and other paid plans. The Export Tool is free for everyone but writes .eml, not mbox. Either way this viewer reads what you end up with at no cost.
Yes. Thunderbird may have helped create the mbox through Bridge, but reading it later needs only a browser. Open this page on any device, pick the file and the messages are listed with their attachments.
In the location you type when it asks, inside a folder named after your address and then a mail_ folder stamped with the date and time of the run. Every .eml and its .json sit in there. Open the folder with Select a folder and the tool lists each message.
Open the export here, pick the messages that matter and save them as .eml. Outlook, Apple Mail and Thunderbird all open .eml with attachments and headers intact. For a whole mailbox at once, the Windows viewer linked above handles bulk export.
Mail you decrypted with Bridge or the Export Tool should stay on your machine. It does here. No server, no upload, no client.
Choose a Proton Mail export