Does every MBOX file use the .mbox extension?

No. RFC 4155 notes that MBOX files may use the .mbox extension but it is not required. Thunderbird local mailbox files, for example, may appear with no extension.

What is the difference between MBOX and PST?

MBOX is a widely used mailbox container format associated with multiple email clients and export systems. PST is Microsoft Outlook's personal storage format. Outlook does not directly use MBOX as its native mailbox data file.

Can Google Takeout create MBOX files?

Yes. Google Takeout is commonly used to export Gmail mail data, and Google documents that exported mail includes message content, headers and attachments. The downloaded mail archive is commonly provided in MBOX form.

Can I open an MBOX file before converting it?

Yes. Use the EdbMails Free MBOX Viewer to inspect supported mailbox content first, then choose PST conversion, another supported file output, Microsoft 365, or Exchange as the next step.

What is a Thunderbird .msf file?

A Thunderbird .msf file is an index file. The corresponding mailbox message store may use the same folder name with no extension. Select the mailbox data file rather than the .msf index when processing archived mail.

Reseller
Products
EdbMails

All-in-one Recovery and Migration
- EDB Recovery and Migration
- OST, PST, MBOX, NSF, EML, MSG
- Office 365, Exchange Migration
- SharePoint, OneDrive & Teams
- Google Workspace Migration
- IMAP Migration
- Duplicate Remover
- EdbMails Data Recovery
- Backup Solutions
All Products
EDB Recovery and Migration

EdbMails lets you recover corrupted, damaged, and offline Exchange EDB files, convert EDB mailboxes to PST format, and directly migrate mailbox data to Office 365 and live Exchange Server.

EDB to PST

Recover corrupted, damaged, offline EDB files and convert Exchange EDB mailboxes to PST file format

Public Folder to Exchange

Migrate public folders from an Exchange offline EDB file to live Exchange Server

EDB to Live Exchange Migration

Directly migrate offline Exchange database (EDB) files to live Exchange server

Archive Mailbox to Office 365

Migrate archive mailboxes from offline EDB files directly to Office 365

EDB to Office 365 Migration

Directly migrate offline Exchange database (EDB) files to Office 365

Public Folder to Office 365

Migrate public folders from an offline Exchange EDB file to Office 365

OST, PST, MBOX, NSF, EML, MSG Export and Migration

EdbMails lets you to recover OST and PST files, export OST, PST, MBOX, NSF, EML, and MSG files to PST files, and directly migrate OST, PST, MBOX, and NSF mailbox data to Office 365 and live Exchange Server.

OST Recovery and Migration

Recover offline OST files, convert OST to PST, and migrate OST to Office 365 and Exchange Server

PST Recovery and Migration

Recover Outlook PST files , Export PST to PST, migrate PST to Office 365 and Exchange Server

MBOX Export and Migration

Export MBOX to PST, migrate MBOX to Office 365 and Exchange Server

NSF Export and Migration

Export NSF to PST, migrate NSF to Office 365 and Exchange Server

EML to PST Export

Convert EML files to Outlook PST files

PST to MSG Export

Convert Outlook PST file to MSG file format

MSG to PST Export

Export MSG files to Outlook PST files

Office 365, Exchange Migration

EdbMails lets you securely migrate mailboxes across Microsoft 365, Exchange, Google Workspace (G Suite), and IMAP-supported servers such as Outlook, Gmail, Zimbra, Zoho Mail, and cPanel, ensuring zero downtime.

Office 365 Migration

Migrate between Office 365 tenants, Office 365 to Exchange, Office 365 to PST, PST files to Office 365.

Exchange Migration

Migrate between any Exchange Servers, Exchange to Office 365, Exchange to PST, PST files to Exchange.

Tenant to Tenant Migration

Migrate Mailboxes, Public Folders, Archive Mailboxes between Office 365 Tenants.

Exchange to Office 365

Migrate Mailboxes, Public Folders, Archive Mailboxes from live Exchange server to Office 365.

Office 365 to IMAP

Migrate Office 365 to IMAP, Office 365 to Gmail, Office 365 to Outlook, Office 365 to Zoho etc.

Exchange to IMAP

Migrate from live Exchange Server to IMAP servers such as Gmail, Outlook, and Zoho Mail.

Public Folder to Office 365

Migrate Public Folders between Office 365 tenants with complete folder hierarchy and mailbox data integrity.

Exchange to PST

Export live Exchange Server mailboxes, public folders, and archive mailboxes to Outlook PST files.

SharePoint, OneDrive & Microsoft Teams Migration

EdbMails lets you migrate SharePoint sites, OneDrive data, Microsoft Teams, teams, channels, chats, permissions, and documents between Microsoft 365 tenants while maintaining the existing folder structure and data integrity.

SharePoint Online Migration

Migrate documents, lists, files and folders from SharePoint sites.

OneDrive for Business Migration

Migrate documents, lists, files, folders, private chats from OneDrive.

Microsoft Teams Migration

Migrate Teams, chats, channels, documents, files and folders etc.

Google Workspace / G Suite Migration

EdbMails offers secure Google Workspace migration to Office 365, Exchange, or IMAP, and export to PST covering emails, contacts, calendars and tasks.

Google Workspace Migration

Migrate emails, calendars, contacts, tasks from Google Workspace to Google Workspace, office 365, Exchange and IMAP. Export to PST

Google Workspace to Office 365

Migrate emails, calendars, contacts, tasks from Google Workspace / G Suite to Office 365

Google Workspace to Exchange Server

Migrate emails, calendars, contacts, tasks from Google Workspace / G Suite to on-Premise Exchange Server

Google Workspace to IMAP

Migrate emails, calendars, contacts, tasks from Google Workspace / G Suite to IMAP, Outlook, Zimbra, Zoho etc.

Google Workspace to Google Workspace

Migrate emails, calendars, contacts, tasks between two Google Workspace / G Suite tenants

Google Workspace to PST

Export emails, calendars, contacts, tasks from Google Workspace / G Suite to Outlook PST files

IMAP Migration

EdbMails IMAP Migration tool lets you easily migrate emails from IMAP servers such as Outlook, Gmail, Zoho Mail, Zimbra, cPanel, and more. Supports IMAP to IMAP, Office 365, Exchange Server, PST, and bulk PST to IMAP migration.

IMAP Email Backup & Migration

Backup and migrate emails from IMAP servers to PST, Office 365, and On-Premises Exchange Server

IMAP to Office 365

Migrate emails, folders, and attachments from IMAP servers to Office 365

IMAP to Exchange

Migrate emails, folders, and attachments from IMAP servers to on-premises Exchange Server

IMAP to PST

Export emails, folders, and attachments from IMAP servers to Outlook PST files for backup

PST to IMAP

Migrate emails, folders, and attachments from bulk PST files to IMAP servers

Duplicate Remover

EdbMails Duplicate Remover lets you easily remove duplicate items from Office 365 and Exchange Server, and from IMAP, Outlook, Gmail, Zimbra, Zoho Mail, etc., ensuring a clean and organized mailbox.

Remove Duplicates

Easily clean up your Office 365, Exchange, Outlook and IMAP accounts by removing duplicate emails.

Remove Duplicates from Office 365

Remove duplicate emails, calendars, contacts, journal tasks, etc. from Office 365.

Remove Duplicates from Exchange Server

Remove duplicate emails, calendars, contacts, journal tasks, etc. from live Exchange Server.

Remove Duplicates from IMAP, Outlook

Remove duplicate emails, attachments from IMAP, Outlook, Gmail, Zimbra, Zoho Mail etc.

Exchange, SharePoint, OneDrive, Teams and Office 365 Backup

EdbMails enables secure, automated backup and recovery for Microsoft 365 services including Exchange Online, SharePoint, OneDrive, Teams, and Live Exchange Server with complete data protection and restore flexibility.

Office 365 Backup

Incremental, Granular, Encrypted and Compressed Office 365 Mailboxes Backup

Exchange Server Backup

Incremental, Granular, Encrypted and Compressed Exchange Mailboxes Backup

SharePoint, OneDrive & Teams Backup

Backup Online site collections, Team sites, Office 365 groups, all documents etc.

EdbMails Data Recovery

EdbMails Data Recovery Software lets you recover permanently deleted data, including photos, videos, documents, and archived files, from partitions on hard drives, SSDs, USB drives, SD cards, and external storage devices.

EdbMails Data Recovery

Recover and restore permanently deleted data from hard drives, SSDs, USB drives, SD cards, and etc.

Whitepaper

Request a Demo

Sign Up

What Is an MBOX File? Email Mailbox Format Explained

Understand the MBOX mailbox file format

Learn how MBOX files store multiple email messages, which applications use the format, and why Thunderbird, Google Takeout and Apple Mail commonly create MBOX archives. Explore practical options to open, convert, or migrate them.

Just $45 Onwards

MBOX to PST Converter MBOX to Office 365 Migration MBOX to Exchange Migration OST to PST Converter NSF to PST Converter EDB to PST Converter

MBOX to PST Converter Now on Azure Marketplace!

Product Menu

What Is an MBOX File? Email Mailbox Format Explained

MBOX is a mailbox database format used to store a sequence of email messages in a single mailbox file. It has a long history on Unix-like systems and is also used or exported by applications and services such as Thunderbird, Apple Mail and Google Takeout. The exact implementation can vary, which is why the source application and intended destination matter when you open, convert or migrate an MBOX archive.

Open an MBOX File

How the MBOX format stores email

RFC 4155 describes MBOX databases as a linear sequence of electronic mail messages. In common implementations, messages are stored one after another and separated by a line that begins with From . Because the format has existed across many platforms and products, there are variations in how different applications write and interpret MBOX data.

That means an MBOX file is usually better understood as a mailbox container rather than a document you double-click like a PDF. An email client or dedicated viewer parses the message boundaries, headers, body content and attachments and then presents the mailbox in a readable interface.

RFC 4155: application/mbox media type

Where do MBOX files come from?

Mozilla Thunderbird

Thunderbird can store local mailbox messages in MBOX-style files that may have no filename extension. The associated .msf file is an index and does not contain the mailbox messages themselves.

Thunderbird to PST

Google Takeout

Google Takeout can export Gmail mail data for archival or transfer. Google documents that exported mail can include message content, headers, attachments and label metadata. The resulting mail archive is commonly delivered as MBOX.

Google Takeout MBOX

Apple Mail and other clients

Apple Mail exports mailboxes as MBOX, and many older or cross-platform email clients also use or export MBOX-family mailbox files. EdbMails supports a wide range of these sources.

Common MBOX file characteristics

One mailbox can contain many messages

Unlike EML, which represents an individual message file, MBOX typically groups many messages together in one mailbox container.

The extension is not always .mbox

RFC 4155 explicitly notes that the .mbox extension is not required. Some applications use files with no extension or other related mailbox extensions.

Formatting can vary by application

Different programs have historically produced MBOX variants. A dedicated viewer or converter should therefore identify and parse the mailbox rather than relying only on the filename.

Attachments are encoded within messages

Attachments travel as part of the underlying email message representation. A viewer or conversion tool needs to parse those message structures to display or export them correctly.

MBOX vs PST vs EML: which is which?

Format	Typical role	Best fit	EdbMails path
MBOX	Mailbox container holding a sequence of messages	Thunderbird, Google Takeout, Apple Mail exports and many legacy clients	View, convert or migrate the MBOX source
PST	Microsoft Outlook personal storage file	Outlook-oriented archive or transfer workflow	MBOX to PST Converter
EML	Individual email message file	Per-message portability and selective handling	MBOX File Converter

What should you do with an MBOX file?

Need only to inspect it?

Open it with the Free MBOX Viewer.

Need Outlook PST?

Use the MBOX to PST Converter.

Need PST, EML, HTML or MHT?

Use the MBOX File Converter.

Need Microsoft 365?

Use the MBOX Migration Tool rather than generating PST solely as an intermediate step.

Need Exchange Server?

Use the MBOX to Exchange Migration Tool.

How to recognize an MBOX mailbox file

.mbox extension

Some exports use a visible .mbox extension. Google Takeout archives and Apple Mail exports are common examples users encounter when moving or archiving mail.

No extension

Thunderbird local mailbox files may use the folder name with no extension. A file named Inbox can contain the mailbox messages while Inbox.msf is only the index.

Related mailbox extensions

Some products use related extensions such as MBX or MBS. Do not assume that a filename alone proves compatibility; preview or test the source with a copy before planning production conversion.

What information can be stored inside an MBOX archive?

An MBOX database stores complete email message representations rather than only subject lines.

Message headers

Email headers can contain sender, recipient, date, subject, message identifiers and routing information. The exact headers present depend on the original messages and source application.

Message body

Plain-text and HTML message bodies are stored as part of each email's underlying MIME representation.

Attachments

Attachments are encoded within the email message structure. A proper viewer or converter decodes them as part of parsing each message.

Application-specific metadata

Some export systems add application-specific headers. Google Takeout, for example, can preserve Gmail label information in export metadata, although other mail applications may not interpret those labels in the same way.

MBOX strengths and practical limitations

Strength

Portable across many tools

MBOX has been used by many email clients and archiving systems, which makes it useful as an interchange or export format.

Limitation

Large archives become unwieldy

A single mailbox file can become very large. Copying, scanning or rebuilding indexes for a large MBOX archive can take significant local storage and processing time.

Limitation

Not a native Outlook format

Microsoft Outlook uses PST/OST data structures rather than MBOX as its native mailbox file format. Users moving to Outlook therefore commonly convert MBOX to PST or migrate the messages through another supported route.

Limitation

Variants exist

RFC 4155 notes historical variation among MBOX implementations. A robust workflow should test representative source data rather than assuming every MBOX-producing application writes exactly the same structure.

Limitation

File damage can affect many messages

Because one mailbox file can contain many messages, corruption or truncation in the source can affect access to a broad portion of the archive. Preserve a backup before manipulating old mailbox files.

Limitation

Folder hierarchy may live outside one file

Applications often represent each folder as a separate MBOX file or use surrounding directory structures. A collection of mailbox files may be needed to reconstruct the user's visible folder organization.

MBOX source examples and the next best action

Google Takeout

What you may receive: Downloaded Gmail mail archive in MBOX form

Recommended next step: View first, then convert to PST or migrate to Microsoft 365 according to the final requirement

Thunderbird

What you may receive: Mailbox files named after folders, sometimes with no extension, plus .msf indexes

Recommended next step: Identify the actual message files, preserve the profile backup, then view or convert

Apple Mail

What you may receive: Exported mailbox archive

Recommended next step: Preview the archive and choose PST or another supported output if moving to Windows/Outlook

Legacy clients

What you may receive: MBOX/MBX/MBS-style archives or mailbox files copied from an old profile

Recommended next step: Test a copy with the viewer, then choose the correct conversion or migration path

The MBOX file in an email lifecycle

MBOX is often an intermediate or archival representation rather than the place where users want to work with mail forever.

Active email client storage

Some email clients use MBOX-style files as local mailbox storage. In that case the file is part of the working profile and should be handled together with the application's folder/profile structure.

Backup or export

Services such as Google Takeout and applications such as Apple Mail can produce MBOX as an export format. The resulting archive is useful for retention or transfer but may not be directly usable by the destination application.

Conversion

When users move to Outlook-oriented storage, converting MBOX to PST changes the mailbox container while preserving supported message content for the new use case.

Migration

When Microsoft 365 or Exchange is the destination, MBOX can be treated as the source archive for a live mailbox migration rather than converted to PST first.

Long-term archive

If the organization intends to retain MBOX itself, document the source application, creation date and expected contents. An archive is more useful when future administrators know how it was produced and how to open it.

Discovery and re-use

Years later, an archived MBOX may need to be opened for a user request, legal hold, historical reference or platform move. A dedicated viewer and clear source documentation make that later re-use easier.

Related MBOX resources

Free MBOX Viewer

Open and inspect the mailbox before deciding on the final destination.

View MBOX File

MBOX File Converter

Convert supported MBOX content to PST, EML, HTML or MHT.

Convert MBOX

MBOX to PST Converter

Use the dedicated workflow when Outlook PST is specifically required.

MBOX to PST

Frequently asked questions

What is an MBOX file?
An MBOX file is a mailbox database that stores a sequence of email messages in one file. The format has been used by many email clients, archiving tools and export workflows.
Does every MBOX file use the .mbox extension?
No. RFC 4155 notes that MBOX files may use the .mbox extension but it is not required. Thunderbird local mailbox files, for example, may appear with no extension.
What is the difference between MBOX and PST?
MBOX is a widely used mailbox container format associated with multiple email clients and export systems. PST is Microsoft Outlook's personal storage format. Outlook does not directly use MBOX as its native mailbox data file.

Can Google Takeout create MBOX files?
Yes. Google Takeout is commonly used to export Gmail mail data, and Google documents that exported mail includes message content, headers and attachments. The downloaded mail archive is commonly provided in MBOX form.
Can I open an MBOX file before converting it?
Yes. Use the EdbMails Free MBOX Viewer to inspect supported mailbox content first, then choose PST conversion, another supported file output, Microsoft 365, or Exchange as the next step.
What is a Thunderbird .msf file?
A Thunderbird .msf file is an index file. The corresponding mailbox message store may use the same folder name with no extension. Select the mailbox data file rather than the .msf index when processing archived mail.