Merge MBOX to PDF: Combine Mailbox Files into One Document

Merge MBOX to PDF combines the emails from several mailbox files into one PDF you can read, search, print or hand over without an email program. Add your .mbox files, and the tool lays out every message on its own pages, after a contents page that lists all the subjects.

It's handy for a mailbox exported in parts, the archives of several people on one project, or a batch of messages you have to send to a lawyer or accountant. You don't need an account.

How to merge MBOX files to PDF

1. Click Choose Files and pick your .mbox files, or drag them onto the page.
2. Check the files shown. They get merged in the order you added them, so to move a file to the end, remove it and add it again.
3. Click Merge MBOX to PDF and wait while the mailboxes upload and the PDF gets built.
4. Download the PDF with all the messages.

What is an MBOX file?

MBOX is a mailbox format that keeps many emails in one plain text file. As the IETF's application/mbox specification (RFC 4155) describes, each message begins with a separator line that starts with "From" and a space, followed by the message itself.

Google Takeout exports Gmail in this format. Thunderbird keeps each local mail folder as an MBOX file named after the folder, such as Inbox or Archive, with no extension, so copy those files out of the profile folder and rename the copies to end in .mbox before you upload them.

What the merged PDF contains

The first page is a cover titled Merged MBOX to PDF. It shows how many email messages the PDF holds, plus a numbered contents list of their subjects.

Each email then starts on a new A4 page, headed Message 1 of 6, Message 2 of 6 and so on, with its headers, its text and the names and sizes of its attachments. Nothing on the page says which mailbox a message came from, so if that matters, note the order of your files.

Merging two Thunderbird folders: duplicates stay in

In October 2026 we merged two Thunderbird style folder files renamed to Inbox.mbox and Archive.mbox. Inbox held 3 messages and Archive 4, and two of them, Invoice 501 and Invoice 502, sat in both folders with the same Message-ID.

The merge doesn't remove duplicates, even with the same Message-ID. Compare the count on the contents page with the sum of your folders. If they match and you still see repeated subjects, delete the copies in your mail program and export again, or drop their pages afterwards.

A single message saved as .mbox

Each mailbox goes to the server as a file of its own, and the server splits every file at the lines starting with "From ". A file with no such line, like a single .eml message renamed to .mbox, gets read as one message.

In our October 2026 test that renamed message kept its place next to test.mbox with three messages. Put first, the PDF listed it as Message 1 of 4; put last, as Message 4 of 4, after Third Email.

Got lots of single .eml messages? Merge Emails to PDF takes them without renaming and mixes them with mailboxes. With the same two files it also listed 4 messages, and the two Thunderbird folders gave the same 7 messages and 8 pages as here.

What happened when we tested Merge MBOX to PDF

We uploaded our small test mailbox test.mbox, 802 B with three short emails, twice. The tool merged them in upload order and returned test_MergedMbox.pdf, 23.6 KB, with 7 pages: the contents page and one page for each of the six messages.

There are no options to set, so the files were merged as uploaded. Tested in October 2026.

Limits of the MBOX merge

All the mailboxes go up in one request, so the files you merge together can be up to 25 MB in total. Two 13.0 MB mailboxes were too much: the page kept the first and showed "Archive-13mb.mbox: not added. All files in one merge can be up to 25 MB together."

Two 11.9 MB mailboxes of 90 messages each, every message with a 100 KB attachment, merged in 5.2 seconds in our October 2026 browser test into 184 pages of 192.4 KB. The contents took pages 1 to 4, Inbox filled pages 5 to 94 and Archive pages 95 to 184. Message n sits on page n plus the contents pages, which tells you where each mailbox starts.

For a bigger archive, split it into batches and join the PDFs you get with Merge PDF; our PDF optimization tools can shrink a long result.

The font covers Latin, Greek and Cyrillic letters. It doesn't cover Chinese, Japanese or Korean characters, so messages in those scripts won't print correctly.

For a single mailbox, MBOX to PDF does the same job for one file, and our guide on how to convert MBOX to PDF covers exporting the mailbox first. To keep just some messages from the result, pull those pages out with Extract PDF Pages.

Frequently Asked Questions about Merge MBOX to PDF

In what order are the emails merged?

File by file, in the order you added the files, and inside each file in the order the messages appear in the mailbox. The tool doesn't sort them by date.

Are duplicate emails removed?

No. A message that's in two of your mailbox files shows up twice, once for each file, even with the same Message-ID.

Can I add a single .eml message to the merge?

Yes, renamed to .mbox. A file without a From line is read as one message in the place you added it, and Merge Emails to PDF takes .eml files as they are.

How large can my mailboxes be?

All the files in one merge together can be up to 25 MB. Split bigger archives into batches.

Can I merge Outlook PST or MSG files?

No. The tool only reads MBOX. Save Outlook messages as .eml files and use Merge Emails to PDF.

How long do you keep my mail?

The uploaded mailboxes and the PDF get deleted automatically within two hours. You don't need an account to use the tool.