Free mbox to PST converter
By Aksel VisbyPublished Updated Tested with ContinuMail Converter v0.3.2
Yes — you can convert mbox to Outlook PST for free. ContinuMail Converter is a free, open-source (GPL-3.0) converter for Windows that runs entirely on your PC, needs no Outlook, and preserves your folders, attachments and — from a Thunderbird profile — your tags and flags. Paid converters add polish, more formats and support, but charge a licence. Here's the honest comparison.
Free · no sign-up · Windows 10/11
Free vs paid, at a glance
| ContinuMail (free & open-source) | Typical paid converter | |
|---|---|---|
| Price | Free, open-source (GPL-3.0) | Paid licence — one-off or subscription |
| Source code | Open and auditable on GitHub | Usually closed-source |
| Where it runs | Entirely on your PC, nothing uploaded | Usually local; some are online/cloud |
| Outlook required to convert | No | Sometimes |
| Thunderbird tags → Outlook categories | Yes, from a profile (with colours) | Often dropped |
| Read/unread, stars, replied/forwarded | Preserved when supplied by the source; profile data is authoritative | Varies by tool |
| Calendars, contacts & tasks | Yes, from a Thunderbird profile | Varies; often mail-only |
| Multiple accounts | One PST each, or combined | Varies by tool |
| Split large PSTs by size | Yes | Often a paid-tier feature |
| Other inputs (PST/OST, Apple Mail, EML) | Thunderbird & mbox today; more on the roadmap | Often broader today |
| Platform | App: Windows 10/11 · CLI: Windows, Linux, macOS | Often Windows; some cross-platform |
| Trial limits | None — fully free | Often a capped trial or watermark |
"Typical paid converter" is a category generalisation — exact features, price and privacy vary by product, so check the specific tool you're weighing up.
Where paid tools are genuinely better
Being fair about it: established paid converters usually support far more input and output formats today — PST/OST, Apple Mail, EML, MSG and more — while ContinuMail does mbox only for now. They're also mature products with a company behind them to raise a support ticket with. If you're doing a one-off migration on a deadline and need a format ContinuMail doesn't handle yet, a paid tool can be the pragmatic choice.
Where ContinuMail wins
It's free and stays free, and because it's open-source you (or anyone) can verify exactly what it does. It runs entirely on your machine, so your mail never leaves your computer and your originals are only ever read, never changed. It needs no Outlook to build the PST. And on fidelity it punches above its price: from a Thunderbird profile it brings across the tags, stars, flags and folder structure that a bare export — and plenty of paid tools — quietly drop.
Which should you pick?
Choose ContinuMail if your mail is in mbox (or a Thunderbird profile), you're on Windows, and you care about it being free, private and faithful — especially if you want your Thunderbird tags and flags to survive the move.
Consider a paid tool if you need a format ContinuMail doesn't support yet, or formal vendor support.
New here? Start with thembox to PST guide, or theThunderbird to Outlook guideif you're switching from Thunderbird. Curious why this is hard to get right? Seehow it works.
Questions people ask
- Is there a genuinely free mbox to PST converter?
- Yes. ContinuMail Converter is free and open-source under the GPL-3.0 licence, with no trial cap, no watermark and no paywalled features. It converts mbox to Outlook PST on Windows, entirely on your own PC.
- Are free mbox to PST converters safe?
- It depends on the tool. The safest combination is open-source plus local-only: you can read the code, and your mail never leaves your computer. ContinuMail is open-source, makes no network connections, and only ever reads your original files.
- Do paid converters preserve more than free ones?
- Not necessarily. Features vary by product. ContinuMail recovers read/unread, stars and replied/forwarded marks when the source supplies them and, from a Thunderbird profile, turns tags into Outlook categories. Paid tools often lead in supporting more input formats.
- When is a paid converter the better choice?
- If you need formats ContinuMail does not handle yet (such as PST/OST or Apple Mail), a code-signed installer for managed environments, or a vendor you can raise a support ticket with, a paid tool may suit you better today.
- Do I need Outlook to convert mbox to PST?
- Not with ContinuMail — it writes the PST with its own engine, so Outlook need not be installed to convert. Some paid tools drive Outlook over automation and require it installed.
Free, open-source, and entirely on your own PC.
Free · no sign-up · Windows 10/11