FAQ
Frequently asked questions
Everything about MBOX files, Thunderbird and Google Takeout exports, Apple Mail archives and how Mbox Viewer works.
What is an MBOX file?
MBOX is a standard format for storing email messages in a single file. Google Takeout exports your Gmail as MBOX, and many email clients and servers use it for backups and archives.
How do I back up my Gmail as MBOX?
Go to takeout.google.com, deselect everything, select only “Mail”, and create the export. Google prepares a .zip archive (it can take hours for large accounts). Download it, unzip it, and open the .mbox file with Mbox Viewer.
Can it open very large files?
Yes. Mbox Viewer uses a streaming parser that never loads the whole file into memory, so it opens archives of 50 GB and beyond. The first open builds an index; every later open is under a second.
Does it modify my MBOX file?
Never. Mbox Viewer is strictly read-only. It creates a small index file next to your MBOX for fast access, but never writes to the original.
What's the difference between Free and Pro?
Free includes every feature but is limited to files up to 500 MB. Pro removes the size limit with a one-time in-app purchase. There is no feature gating — search, export, labels and threading all work in both.
Is there a subscription?
No. Pro is a single one-time purchase through the Mac App Store. No subscription, no account, no recurring charges.
Does it support HTML emails?
Yes. Mbox Viewer renders HTML emails with their original formatting. For privacy, remote images are blocked by default, with an option to load them, and message HTML is sanitized before display.
Which macOS versions are supported?
macOS 14 Sonoma and later. It's a Universal Binary that runs natively on Apple Silicon (M1–M4) and Intel Macs.
Is there a Windows version?
Not yet. Mbox Viewer is a native macOS app today, and a Windows version for the Windows app store is on the roadmap.
Does my data leave my Mac?
No. Everything runs locally — no cloud, no telemetry, no account. Your emails never leave your machine.
How do I open a Thunderbird mbox file on Mac?
Thunderbird stores each mailbox (Inbox, Sent…) as a standard mbox file without a file extension. Find it in your Thunderbird profile folder, make a copy, add the .mbox extension to the copy and open it with Mbox Viewer. Files exported with add-ons like ImportExportTools NG already have the extension and open directly.
How do I open an Apple Mail export (.mbox folder)?
Apple Mail exports a folder named “YourMailbox.mbox” that contains a file called simply “mbox” — that inner file holds your messages in standard mbox format. Open that “mbox” file with Mbox Viewer (drag & drop works too).
Can I view my Gmail / Google Takeout export?
Yes. Google Takeout delivers your Gmail as a standard .mbox file that Mbox Viewer opens directly — including your Gmail labels, which show up in the sidebar. Unzip the Takeout archive and open the .mbox file inside.
Can I open Outlook emails (PST / OLM)?
Not directly — Outlook stores mail in PST/OLM, which isn't mbox. Convert the file to mbox with a converter tool first, then open the result with Mbox Viewer.