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EML MBOX
File conversion

Convert EML to MBOX

Verified by Adam B.· reviewed by FE Editorial ·updated Aug 14, 2026
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Is it possible to convert EML to MBOX?
Yes - EML converts to MBOX.

Install ImportExportTools NG in Thunderbird, right-click Local Folders, and import a directory of .eml files; Thunderbird writes all messages into an mbox mailbox on disk. The only caveat is that Thunderbird must be installed - no standalone converter exists for this task.

Also to MBOX: BOX · TOC · NSF

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Tested on macOS, Windows & Linux
Last verified Oct 2026

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Why convert EML to MBOX?

MBOX (RFC 4155) is a plain-text container that concatenates many email messages into a single file, used as a mailbox folder by clients such as Thunderbird, Apple Mail, and Evolution. If you have individual .eml files from an export or old account, importing them as a single .mbox makes them searchable and browsable inside a mail client rather than sitting as isolated files on disk.

How to convert EML to MBOX

Mozilla Thunderbird + ImportExportTools NG FREE

In Thunderbird, install the ImportExportTools NG add-on, right-click Local Folders, and choose ImportExportTools NG > Import EML files > All EML files from a directory. Thunderbird writes all messages into an mbox mailbox file under your Thunderbird profile folder.

About these formats

.EML E-Mail Message (RFC 822 / MIME)

An EML file is one email message saved as a plain-text file - headers, body, and any attachments - in the internet-standard MIME/RFC 822 format. You do not need Microsoft Outlook to open…

Open .EML details →
.MBOX Mbox Mailbox (email container)

An MBOX file is a mailbox - a single plain-text file that holds many email messages stored one after another. Google Takeout exports Gmail as .mbox, and Thunderbird and Apple Mail use the…

Open .MBOX details →

Quality & what to watch

  • All message headers, HTML and plain-text body parts, and attachments survive the conversion - MBOX stores messages in the same MIME format as .eml, so nothing is re-encoded.
  • Each message in the resulting mbox file is preceded by a From separator line (with a trailing space); this is standard mbox format expected by all compatible clients.
  • The mbox file Thunderbird creates has no file extension by default - add .mbox if you need to identify it when moving it to another mail client.

Frequently asked questions

Do I need to keep Thunderbird installed to use the mbox file?
No - once created, the mbox file can be opened by any compatible client such as Apple Mail or Evolution without Thunderbird.
Can I import a single `.eml` file rather than a whole folder?
Yes - ImportExportTools NG lets you import individual .eml files or an entire directory at once.
Where does Thunderbird save the mbox file on disk?
Under your Thunderbird profile in a Mail/Local Folders/ subfolder; the file has the folder name with no extension.