Open an .mbox file

What an mbox file is

An .mbox is a whole mailbox in one file: every message, one after another, each starting with a line that begins From . It is what Google Takeout gives you for Gmail (in Takeout, Mail, usually called All mail Including Spam and Trash.mbox), what Apple Mail writes when you choose Mailbox, Export Mailbox, and what Thunderbird keeps its folders in. Most computers have nothing that opens one, and the usual advice is to import it into a mail program or buy a converter.

How it is read

• Listed in one pass. The file is read once and only each message's headers are kept, with where the message sits in the file. A mailbox of several gigabytes is listed without being held in memory, and a message is read from the file again when you open it.
• Straight from the Takeout zip. There is no need to unzip it first. Every mailbox in the zip is read, the mail and the chats alike, and several .mbox files dropped together are listed side by side, each a mailbox of its own.
• By label and by conversation. Gmail’s labels are listed down the side, Inbox and Sent first. An email opens with the rest of its conversation listed above it, from Gmail’s thread or, in other mailboxes, from the References header every mail program writes. Unread, starred and important come from Gmail’s labels, Thunderbird’s own flags or the mbox Status header.
• Searched to the text. Search finds who sent an email, who it went to, its subject and its labels; tick “Search the text of each email too” and it reads each email as well, showing the words it found. Put a phrase in quotes to find it as a phrase. On a keyboard, / goes to the search, j and k open the next and the previous email, and Escape goes back to the list.
• Each message read in full. Opening one reads its parts, character sets, encoded subjects and attachment names with the same parser MAILBOX uses for a single email, and shows MAILBOX’s warnings about it, such as failed authentication. An email forwarded as an attachment opens in place.
• Nothing in an email runs or reports back. An HTML email is shown in a sealed frame. Scripts, forms and frames are taken out, links do nothing, and pictures that live on the internet are not loaded, since loading one tells the sender the email was opened, and when. Pictures sent inside the email are shown. Printing uses a frame sealed the same way.
• Saved as you need it. Any message saves as an .eml, which Apple Mail, Outlook and Thunderbird all open, exactly as it is in the mailbox. What the list shows (a label, a search) saves as its own .mbox, as a .zip of .eml files, or as a .zip of every attachment in it; every label can save as its own .mbox in one .zip; and the list saves as a CSV.

What it does not do

An email encrypted with S/MIME or PGP stays encrypted; a signed one can be checked in SIGNET. To follow where a message really came from hop by hop, open it in MAILBOX, which reads its delivery path and authentication results in full.