MailtoPst
FR
OLM MBOX

Convert OLM to MBOX
Online Tool

Convert Outlook for Mac OLM files to MBOX format online. Migrate from Outlook Mac to Thunderbird, Apple Mail, or any MBOX-compatible client. EU servers, GDPR compliant.

Convert now → See how it works
🛡️ GDPR Compliant 🔒 TLS 1.3 Encryption 🇪🇺 Hosted in EU 🇫🇷 Built in France 🗑️ Auto-delete 24h

What is a OLM file?

OLM (Outlook for Mac) is the archive format created exclusively by Microsoft Outlook on macOS. When you export data from Outlook for Mac (2011, 2016, 2019, or Microsoft 365 for Mac), it generates an .olm file — a ZIP-based container holding emails, contacts, calendar items, tasks, and notes.

Key characteristics of OLM files:
- Mac-only format — created and read only by Outlook for Mac
- ZIP-based structure — internally contains XML metadata and EML-like email files
- Complete data export — includes all mailbox data types (email, calendar, contacts)
- No Windows support — cannot be opened by Outlook for Windows or any non-Mac application
- Single-file archive — all exported data is packaged in one .olm file

OLM files are typically created when users want to back up their Outlook for Mac data, migrate to a new computer, or switch to a different email client.

What is a MBOX file?

MBOX (Mailbox) is one of the most universally supported email storage formats. It stores multiple email messages in a single text file, with each message separated by a 'From ' line marker, following internet email standards.

MBOX is the preferred format for:
- Mozilla Thunderbird — uses MBOX as its native storage format
- Apple Mail — can import and export MBOX files natively
- Gmail Takeout — Google exports Gmail data in MBOX format
- Unix/Linux mail systems — standard format for Postfix, Dovecot, and other servers
- Email migration tools — widely accepted as input by server-side import utilities
- Long-term archival — open, text-based format suitable for preservation

By converting OLM to MBOX, you transform a Mac-only proprietary archive into a universally readable format.

Why convert OLM to MBOX?

Converting OLM to MBOX is essential in several scenarios:

1. Migrating to Mozilla Thunderbird
Thunderbird uses MBOX natively. Converting OLM to MBOX is the most direct path to importing your Outlook for Mac emails into Thunderbird on any operating system.

2. Switching from Mac to Linux
Linux users moving from macOS need their email data in a format that Linux email clients can read. MBOX is the standard format on Linux and is supported by Thunderbird, Evolution, and KMail.

3. Importing into Apple Mail
Apple Mail has a built-in MBOX import feature (File > Import Mailboxes). Converting OLM to MBOX provides a clean import path for users staying on Mac but switching from Outlook to Apple Mail.

4. Server-side email import
System administrators can import MBOX files directly into Dovecot, Zimbra, or other IMAP servers using server-side tools. This is faster than client-side import for large archives.

5. Cross-platform archival
MBOX files are readable on every operating system and will remain accessible for decades. Converting OLM to MBOX future-proofs your email archive against format obsolescence.

OLM vs MBOX — Key Differences

Feature OLM MBOX
Platform macOS only Any OS (Windows, Mac, Linux)
Format ZIP-based binary archive Text-based sequential storage
Client support Outlook for Mac only Thunderbird, Apple Mail, many others
Openness Proprietary Microsoft format Open standard (RFC 4155)
Data types Email + calendar + contacts + tasks Email messages only
Server import Not supported Supported (doveadm, mb2md, etc.)

3 methods to convert OLM to MBOX

Method 1: Manual conversion via email client

Open the OLM file in Outlook for Mac, configure a local Thunderbird or Apple Mail instance, then drag-and-drop emails between clients. Export the emails as MBOX from the receiving client.

Pros

  • ✓ Free if you have the software
  • ✓ Full control over the process

Cons

  • ✗ Requires Outlook for Mac installed
  • ✗ Multi-step manual process
  • ✗ Time-consuming for large archives
  • ✗ Risk of data loss during manual steps

Method 2: Desktop conversion software

Several desktop converters can handle OLM to MBOX conversion locally. These tools run on macOS or Windows and process the OLM file on your machine.

Pros

  • ✓ Direct conversion
  • ✓ Works offline

Cons

  • ✗ Paid ($29-$99)
  • ✗ Platform-specific
  • ✗ Installation required
  • ✗ Limited support and updates
Recommended

Method 3: MailtoPst (online, free trial)

Upload your OLM file to MailtoPst, select MBOX as the output format, and download the converted files. Works from any browser on any operating system. No Outlook required.

Pros

  • ✓ First conversion free
  • ✓ No Outlook for Mac needed
  • ✓ Works on Mac, Linux, Windows
  • ✓ Preserves folder structure
  • ✓ GDPR compliant, EU servers

Cons

  • ✗ Requires internet connection
  • ✗ Paid after first conversion
Try MailtoPst →

Step by step

How to convert OLM to MBOX with MailtoPst

01

Upload your OLM file

Drag & drop or click to upload your .olm file. Files up to 51 GB supported with resumable upload.

02

Choose MBOX as output

Select MBOX from the format dropdown. MailtoPst auto-detects the best conversion settings.

03

Download your MBOX file

Conversion takes seconds. Download your .mbox file or receive it by email.

Convert your OLM to MBOX now →

100 MB free credit. No credit card required.

FAQ

Frequently Asked Questions

Can I convert OLM to MBOX without Outlook for Mac?

Yes. MailtoPst reads OLM files server-side — you don't need Outlook for Mac installed. Upload the OLM file from any browser on any operating system and download the MBOX output.

Will my email attachments be preserved?

Yes. MailtoPst preserves all attachments, email headers, timestamps, and formatting during the OLM to MBOX conversion. The MBOX output is a faithful representation of the original emails.

Can I import the MBOX into Thunderbird?

Yes. MBOX is Thunderbird's native storage format. Use the ImportExportTools NG add-on or copy the MBOX file to Thunderbird's profile folder. The emails will appear as a folder in Thunderbird.

What about calendar and contacts in the OLM?

The OLM to MBOX conversion focuses on email messages. Calendar data and contacts from the OLM file are not included in the MBOX output, as MBOX is an email-only format. Export calendar as ICS and contacts as VCF separately.

How large can my OLM file be?

MailtoPst supports OLM files up to 50 GB with resumable upload technology. If your connection drops during upload, you can resume where you left off. Files are auto-deleted from EU servers within 24 hours.

Related conversions

MBOX → EML MBOX → PST OLM → IMAP OLM → PST PST → MBOX
See all 30 conversion paths →

Ready to convert your emails?

First conversion free. No credit card required.

Start converting → See pricing