Two Very Different Approaches to Email Storage
PST and EML represent two fundamentally different philosophies for storing email. PST bundles an entire mailbox — potentially thousands of messages across dozens of folders — into a single binary database file. EML stores each message as an individual text file following the MIME standard. Understanding when each approach makes sense is essential for email migration, archiving, and disaster recovery planning.
Format Comparison at a Glance
| Feature | PST | EML |
|---|---|---|
| Scope | Entire mailbox (emails, contacts, calendar) | Single email message |
| Structure | Binary database (MS-PST spec) | Plain text (MIME/RFC 5322) |
| File count | One file for all data | One file per message |
| Primary client | Microsoft Outlook | Thunderbird, Apple Mail, and most others |
| Human readable | No | Yes (text editor viewable) |
| Max size | 50 GB per file | No formal limit per file |
| Contains contacts/calendar | Yes | No (email only) |
When PST Excels
Centralized Archiving
PST’s single-file design makes it convenient for backing up or transporting an entire mailbox. Instead of managing thousands of individual files, you have one .pst file that contains everything — emails, folder structure, contacts, and calendar events. This simplifies storage, transfer, and backup operations.
Outlook Integration
If Outlook is your primary email client, PST is the native format. Opening a PST file in Outlook gives you immediate access to the full folder hierarchy with search, filtering, and all Outlook features. No import step is required.
Size Efficiency
Because PST uses a binary database structure with internal compression and shared data blocks, a PST file is often smaller than the equivalent set of EML files. The binary format eliminates the overhead of repeating MIME headers and Base64 encoding across thousands of individual files.
When EML Excels
Universal Compatibility
EML files work with virtually every email client on every platform. Thunderbird, Apple Mail, Windows Mail, eM Client, and dozens of others open EML files without any conversion. PST files require Outlook or a conversion tool.
Granular Control
With EML, each message is an independent file. You can search, sort, copy, move, or delete individual emails using standard file management tools. This is invaluable for selective archiving, legal review, or when you only need specific messages from a large archive.
Transparency and Auditability
EML files are plain text. You can open them in a text editor and inspect the complete message structure — headers, MIME parts, encoding, and attachments. This transparency is important for forensic analysis, compliance audits, and legal proceedings where the authenticity of email evidence must be verifiable.
Programmatic Processing
Developers and IT teams working with automated email processing pipelines find EML easier to handle. Standard libraries in Python, Node.js, and other languages parse MIME/EML natively. PST parsing requires specialized libraries that understand the complex binary format.
Converting Between PST and EML
MailtoPst makes it easy to move between formats:
- PST to EML — extract every message from a PST into individual EML files, organized in folders.
- EML to PST — combine a collection of EML files into a single PST archive for Outlook.
Both conversions preserve all message content, headers, attachments, and timestamps. Processing is secure (TLS encryption, EU servers, auto-delete) and fully GDPR compliant.
Upload your file now and convert in either direction. Try free — no credit card required.
Frequently Asked Questions
Can I open PST files without Outlook?
Not natively on most systems. You can upload the PST to MailtoPst to browse it online or convert to EML for universal access. See How to open PST without Outlook.
Do EML files support attachments?
Yes. Attachments are embedded in the EML file as Base64-encoded MIME parts. When you open the EML in any email client, the attachments appear exactly as they would in the original message.
Which format is better for legal eDiscovery?
EML is generally preferred for eDiscovery because each message is a self-contained file with complete headers, making it easy to authenticate, hash, and present as evidence. PST files can also be used but require Outlook or specialized review tools to access individual messages.
Can a PST file contain EML files as attachments?
Yes. If the original email had an EML file attached to it (a forwarded email as an attachment, for example), the PST stores that EML as an attachment within the message. Converting the PST to EML with MailtoPst preserves these nested attachments.
Is there a quality loss when converting PST to EML?
No. The conversion is lossless for email content. Every header, body section, and attachment is preserved. The only data that does not carry over to EML is non-email PST content like contacts and calendar events, since EML is an email-only format.
Upload your file now to convert between PST and EML.