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Open an .mbox file

Drop a Gmail Takeout .mbox, or the zip it came in, and read every email in it: listed, searchable, and opened with its pictures and attachments. Nothing is imported or uploaded.

The mailbox

Drop an .mbox file here, or the Google Takeout .zip it came in

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. The mailbox is unpacked as it is read into storage the browser keeps for this tab.
  • 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.
  • 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.
  • Any message can be saved as an .eml, which Apple Mail, Outlook and Thunderbird all open, and any attachment can be saved on its own. The list, or just the messages a search found, saves as a CSV.

What it does not do

Search covers who sent each message, who it went to, its subject and its Gmail labels, not the text inside, since reading every message's body would mean decoding the whole file again. Messages are not threaded into conversations. An email encrypted with S/MIME or PGP stays encrypted. To check where a message really came from, save it as an .eml and open it in MAILBOX, which reads its delivery path and authentication results.

Questions people ask about POSTBAG
How do I open an .mbox file?

Drop it on this page. POSTBAG lists every email in it, lets you search by sender, recipient, subject or Gmail label, and opens any message with its text, pictures and attachments. Nothing is installed and the file is not uploaded.

How do I open the mbox file from Google Takeout?

Drop the Takeout .zip on this page as it is, or the .mbox inside it, which is in Takeout, Mail and usually called All mail Including Spam and Trash.mbox. Gmail's labels are read too, so you can pick a label to see only those messages.

Can I open an mbox file without Thunderbird or Apple Mail?

Yes. POSTBAG reads it in a browser tab on Windows, Mac, Linux or a phone, without importing it into a mail program. Any message can be saved as an .eml, which every mail program opens.

Can it open a very large mbox file?

Yes. It reads the file once and keeps only each message's headers, so a mailbox of several gigabytes is listed without being held in memory. Each message is read from the file again when you open it.

Is it safe to open old emails from an mbox?

Here, yes: nothing in an email runs, links do not go anywhere, and pictures on the internet are not loaded, so no sender learns the email was opened. Attachments that run code when opened are flagged.

How do I get attachments out of an mbox file?

Open the message and save each attachment on its own, or save the whole message as an .eml. Attachments are decoded from the email exactly as they were sent.

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