Import MBOX into Thunderbird — the free way, step by step
Mozilla Thunderbird is free and handles .mbox natively via the ImportExportTools NG add-on. Below is the honest walkthrough — and if you'd rather not install anything, the viewer further down opens your file right now, in your browser.
Method 1: Import into Thunderbird with ImportExportTools NG (free)
- Download and install Mozilla Thunderbird from thunderbird.net (free, open source). You don't need to add an email account — skip the account setup.
- In Thunderbird, open Menu → Add-ons and Themes, search for "ImportExportTools NG", and install it.
- In the folder pane, right-click Local Folders and choose ImportExportTools NG → Import mbox file.
- Pick "Import directly one or more mbox files" and select your .mbox file.
Choose "import a copy of the mbox file's messages as individual .eml files" only if you specifically want .eml per message — the direct import is what most people want.
- The mailbox appears under Local Folders — browse, read, and search it like any Thunderbird account.
That method is genuinely free and works well for keeping the mail long-term. Its downsides: the install + add-on dance takes a few minutes, and very large mailboxes can be slow to index.
What ImportExportTools NG is — and when you don't need it
ImportExportTools NG is the standard free, open-source Thunderbird add-on for moving mail in and out of the program: it imports .mbox files and individual .eml messages, exports folders back to .mbox, and saves messages as .eml / .html / .pdf. If Thunderbird is where the mail should live, it is the right tool — install it only from inside Thunderbird (Menu → Add-ons and Themes), so you get the genuine one from the official catalog.
If you landed here searching for the add-on itself, the honest comparison:
| ImportExportTools NG path | Online viewer (this page) | |
|---|---|---|
| Install | Thunderbird + the add-on | None — runs in the browser tab |
| Time to first message | A few minutes of setup | Seconds — drop the file, done |
| Best for | Keeping the mailbox long-term, replying, uploading via IMAP | Peeking inside an archive, searching, grabbing an attachment, CSV/PDF export |
| Your file | Imported into your Local Folders profile | Read-only, parsed locally — never leaves your device |
| Multi-GB mailboxes | Import and indexing can be slow | Streamed in chunks — GB-scale opens fine |
A common failure mode: the import hangs or crawls on a multi-GB archive, because Thunderbird re-indexes the whole file. The viewer below streams the file instead of importing it — and exports a CSV or merged PDF of exactly the messages you pick.
Method 2: don't install anything — view it online
If you just want to look inside an .mbox file — check what's in an old archive, find one message, export a metadata CSV or a merged PDF — drop it here. It's read locally in your browser; the file never leaves your device.
Drag & drop your .mbox file here
or
Your file never leaves your device — everything is parsed locally in your browser.
Messages
License active ✓ Keep this key to yourself — abnormal usage will get it deactivated.| # | Date | From | Subject | Size | Att. |
|---|
Message
- From
- To
- Cc
- Date
Attachments
Simple pricing
Viewing and CSV export are free. A one-time $9.99 unlocks PDF export forever.
Free
$0
- Open mbox files of any size
- Read every message, download attachments
- Instant search over From / To / Subject
- CSV metadata export — no account, no upload
Lifetime license
$9.99 one-time · forever
- Merged PDF export of whole mailboxes
- Scope: all, search results, or selected messages
- Pay once, use forever — no subscription
- Support a small independent tool
By purchasing you agree to the Terms of Service and Privacy Policy. Full refund within 14 days if it can't handle your file.
Frequently asked questions
Does Thunderbird open .mbox files without add-ons?
Not directly — Thunderbird stores its own Local Folders as mbox internally, but there is no built-in "open .mbox" command. The free ImportExportTools NG add-on is the standard, well-maintained way to import them.
Is ImportExportTools NG safe and free?
Yes — it's a long-standing, widely used open-source add-on distributed through Thunderbird's official add-on catalog. Install add-ons only from inside Thunderbird (Menu → Add-ons) to get the genuine one.
When should I use Thunderbird instead of this online viewer?
Use Thunderbird if you want to keep and manage the mailbox long-term, reply to messages, or re-upload the mail to an account via IMAP. Use the online viewer above when you just want to peek inside, search, download an attachment, or export a CSV/PDF — with zero installation.
Is the online viewer private?
Fully. The file is parsed by JavaScript in your browser tab; nothing is uploaded to any server. Thunderbird is local too — both methods keep your mail on your machine.
Do I have to import the file into Thunderbird just to read it?
No. Importing makes sense when you want to keep the mailbox in Thunderbird. To just read messages, search, or download an attachment, the online viewer above reads the .mbox as-is — no install, no changes to any mail profile.
ImportExportTools NG is stuck importing my large .mbox — what now?
Multi-GB imports can crawl or look hung while Thunderbird re-indexes everything. If you only need to read, search, or export part of it, drop the file in the viewer above — it streams the file instead of importing it, so big archives still open quickly, and you can export just the messages you select as CSV or PDF.