The Problem: Your Email Backup Is in the Wrong Format
Email backups often outlast the software that created them. You might have a five-year-old PST backup from when you used Outlook, but now you are on Thunderbird. Perhaps a colleague sent you an MBOX export from their Mac, and you need to view it in Outlook. Or your company’s email archiving system produced files in a format your current email client does not support.
Whatever the scenario, the underlying challenge is format mismatch. The emails are safe in the backup, but you cannot access them without converting to a format your current tools understand.
Solution: Convert Between Any Major Email Format
MailtoPst supports conversions between all the major email archive formats. Here is a guide to identifying your backup format and converting it.
Step 1: Identify Your Backup Format
.pst— Microsoft Outlook archive. Contains emails, contacts, calendar, tasks..ost— Outlook offline cache. Bound to a specific profile; needs conversion to PST first..mbox(or.mbx) — Universal text-based archive used by Thunderbird, Apple Mail, and many others..eml— Individual email messages in MIME format. One file per message..msg— Microsoft’s per-message format used by Outlook.
Step 2: Choose Your Target Format
| You want to use… | Best target format |
|---|---|
| Microsoft Outlook | PST |
| Mozilla Thunderbird | MBOX or EML |
| Apple Mail | EML or MBOX |
| Gmail (via IMAP) | EML or MBOX |
| Archival / eDiscovery | EML |
| Any email client | EML |
Step 3: Convert
- Go to mailtopst.com and select the appropriate conversion:
- Upload your backup file.
- Download the converted output and open it in your preferred email client.
All conversions preserve message content, attachments, headers, and timestamps. Files are encrypted via TLS, processed on EU servers, and auto-deleted. GDPR compliant.
Why MailtoPst for Backup Conversion
- All formats covered — PST, OST, MBOX, EML, MSG, and more. No need for multiple tools.
- Metadata preservation — original dates, read/unread status, folder structure, and message flags are maintained.
- Batch processing — convert entire archives in one operation, not message by message.
- Secure handling — TLS encryption in transit, EU-based processing, automatic deletion. Your backup data stays private.
- No installation — everything runs in your browser on any OS.
Try free — no credit card required. Upload your backup and get 100 MB of free conversion credit.
Common Backup Conversion Scenarios
Restoring Old Outlook Backups on a New System
You formatted your computer and reinstalled Outlook, but the PST backup from your old system needs to be imported. Open Outlook, go to File, then Open & Export, then Open Outlook Data File, and select the PST.
Moving From Outlook to Thunderbird
Convert your PST backup to MBOX using PST to MBOX. Import the MBOX into Thunderbird using ImportExportTools NG. See why convert PST to MBOX.
Consolidating Multiple Backup Formats
Over the years, you may have accumulated backups in different formats. Convert everything to a single format (EML is the most universal) for consistent long-term storage.
Making Backups Accessible for Legal Review
Legal teams often need to review email backups during litigation. Converting to EML creates individual files that can be indexed, searched, and presented as evidence in standard eDiscovery tools.
Frequently Asked Questions
Will I lose any data during conversion?
Email messages, attachments, and headers are fully preserved in all conversions. Non-email data (contacts, calendar events) is only preserved when converting between formats that support them (e.g., PST to PST or OST to PST).
Can I convert a backup that is several years old?
Yes. MailtoPst handles PST files from all Outlook versions (97 through Microsoft 365) and MBOX files from any source. Age does not affect conversion quality.
How do I verify the conversion was successful?
Open the converted file in your target email client and spot-check a few messages. Verify that subject lines, dates, body content, and attachments match the originals.
Can I convert password-protected backups?
Yes, for PST files with standard password protection. Enter the password when prompted during upload. See How to convert a password-protected PST.
What is the maximum file size for backup conversion?
The free tier supports files up to 100 MB. Paid plans handle up to 50 GB — large enough for most email archives. See How to convert large PST files.
Upload your file now and restore access to your email backup.