How to use the MBOX viewer
- Point the viewer at your mailbox: choose the .mbox with the button above, or drop it there straight from your downloads folder.
- Wait while the mailbox is indexed. A progress bar shows how far it has got; the file is read in pieces, so large mailboxes work.
- Type in the search box to filter the list by subject or sender, then click a message to read it, download its attachments or press “Save as PDF”.
What is an MBOX file?
An MBOX file is a whole mailbox stored in one file. The messages sit one after another as text, and each one begins with a line starting with the word “From” followed by a space. A mail program finds where one email ends and the next begins by looking for those lines.
The format is decades old and comes from Unix mail systems. It was never pinned down as one strict standard, so there are a few slightly different variants.
You are most likely to have one from one of these:
- Gmail Takeout, Google’s export, which delivers your mail as .mbox.
- Thunderbird, which by default keeps each mail folder as an MBOX file with no extension in its profile folder.
- Apple Mail, whose mailbox export creates a folder ending in .mbox with a file named mbox inside. That inner file is the one to open.
Files with no extension are accepted as they are, so a Thunderbird folder file does not need renaming.
How do I get an MBOX file from Gmail Takeout?
Ask Google Takeout for an export of Mail, then download and unzip the archive Google prepares.
- Sign in to Google Takeout with the account whose mail you want.
- Deselect all the products, then tick Mail. You can limit the export to chosen labels.
- Create the export. Google emails you a download link when it is ready, which can take hours or longer for a big mailbox.
- Download the archive and unzip it. The .mbox file is inside the Takeout folder, under Mail.
What is inside a Gmail Takeout MBOX?
It holds every message in the export, attachments included. Unless you chose specific labels, that is one file covering all your mail, sent messages too.
Gmail labels are not folders, so the export does not split mail by label. Each message carries its labels in a header line named X-Gmail-Labels.
What can I do with a very large MBOX file?
Try opening it as it is. The viewer reads the file piece by piece and does not load it all into memory at once, so multi-gigabyte mailboxes can work. The limit is your device’s memory, not a fixed size.
If it struggles:
- Use a computer and not a phone or tablet.
- Close other tabs and programs to free memory.
- Go back to Takeout and export only the labels you need, which gives a smaller file.
Each message inside an MBOX is an ordinary email in the same format as an .eml file. For a single saved email, the EML viewer opens it without the indexing step.