What Are EML Files and How to Open Them

Published on March 12, 2026

· Updated on March 16, 2026

toolstechnical

If you've ever downloaded an email, received a .eml file as an attachment, or tried to migrate your emails between providers, you've likely encountered the EML format. Despite being one of the most common email file types, many people aren't sure what EML files are, how to open them, or why they matter.

In this guide, we'll cover everything you need to know — from the basics of the EML format to advanced use cases like email forensics and data migration.

What is an EML File?

An EML file is a standard email message format that stores a single email message as a plain text file. The .eml extension stands for "electronic mail," and the format has been around since the early days of the internet.

Each EML file contains the complete email, including:

Headers: All technical and human-readable headers — From, To, CC, BCC, Subject, Date, Message-ID, and dozens of other fields
Body: Both the plain text and HTML versions of the email content (if the sender included both)
Attachments: Any attached files, encoded within the EML using MIME (Multipurpose Internet Mail Extensions) encoding — typically Base64
Inline images: Images embedded in the email body, also MIME-encoded
Authentication headers: SPF, DKIM, and DMARC results added by receiving servers

EML files follow the RFC 5322 standard (and its predecessor, RFC 2822), which defines the format of internet email messages. This standardization makes EML files universally compatible across email clients and operating systems.

What Does an EML File Look Like Inside?

If you open an EML file in a text editor, you'll see something like this:

From: John Smith <john@example.com>
To: Jane Doe <jane@example.com>
Subject: Project Update
Date: Mon, 15 Jan 2026 10:30:00 -0500
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="boundary123"

--boundary123
Content-Type: text/plain; charset="UTF-8"

Hi Jane, here's the project update...

--boundary123
Content-Type: text/html; charset="UTF-8"

<html><body><p>Hi Jane, here's the project update...</p></body></html>

--boundary123--

The file starts with email headers (one per line), followed by a blank line, and then the message body. For emails with both plain text and HTML versions (which is most modern emails), the body is divided into multiple MIME parts separated by boundary strings.

Attachments appear as additional MIME parts with Base64-encoded content — which is why raw EML files can be quite large for emails with attachments.

EML vs. Other Email File Formats

EML isn't the only email file format you might encounter. Here's how it compares to the alternatives:

EML vs. MBOX

Feature	EML	MBOX
Emails per file	One	Multiple
File extension	.eml	.mbox
Standard	RFC 5322	RFC 4155
Best for	Individual emails	Mailbox exports / archives
Readability	Easy to inspect	Harder (concatenated emails)

MBOX files store multiple emails in a single file, separated by "From " lines. They're commonly used for full mailbox exports from providers like Gmail (via Google Takeout) or Thunderbird. If you need to view MBOX files, check out our free MBOX Viewer tool.

EML vs. MSG

Feature	EML	MSG
Format	Plain text (RFC 5322)	Binary (Microsoft proprietary)
Created by	Any email client	Microsoft Outlook
Compatibility	Universal	Primarily Windows/Outlook
File size	Generally smaller	Generally larger
Metadata	Standard headers	Includes Outlook-specific properties

MSG files are Microsoft Outlook's proprietary format. They contain the same email data but in a binary format that's harder to work with outside the Microsoft ecosystem. If you receive an MSG file and don't have Outlook, you'll need a converter or specialized viewer.

EML vs. PST

PST (Personal Storage Table) files are another Microsoft format, but unlike MSG files (which store individual emails), PST files store an entire mailbox — including emails, contacts, calendar entries, and tasks. They're used for Outlook backups and archives.

Common Use Cases for EML Files

Email Archiving and Compliance

Many organizations are required to archive business communications for compliance purposes. Regulations like SOX (Sarbanes-Oxley), GDPR, HIPAA, and industry-specific rules often mandate that emails be preserved for specific periods.

EML files are ideal for archiving because:

Each email is a self-contained file that can be stored independently
The format preserves all original headers and metadata
Files can be organized in folder structures that mirror mailbox organization
The plain text format ensures long-term readability — no proprietary software needed to open them decades later

Email Forensics and Investigation

Security professionals and investigators regularly work with EML files to:

Investigate phishing attempts: Examine the full email headers to trace the origin of a phishing email, checking for spoofed addresses and suspicious routing
Track email origins: Follow the Received headers to trace the path an email took across servers
Examine authentication results: Check SPF, DKIM, and DMARC headers to verify whether the email passed authentication
Analyze malicious attachments: Extract and examine attachments in a controlled environment
Preserve evidence: Maintain the original email in an unmodified format for legal proceedings

Email Migration

When moving between email providers — from one Google Workspace account to another, from Exchange to Gmail, or from a local mail client to a cloud service — EML files serve as a universal transfer format.

The migration process typically involves:

Exporting emails as EML files from the source system
Transferring the files to the destination
Importing the EML files into the new email system

Because EML is standardized, this approach works across virtually any combination of email providers.

Legal Discovery (eDiscovery)

In legal proceedings, emails are frequently requested as evidence. EML files are the preferred format for eDiscovery because they:

Preserve the complete email exactly as it was sent and received
Include all headers that can verify authenticity
Can be verified against DKIM signatures to prove the email hasn't been modified
Are widely accepted by courts and legal professionals

Backup and Personal Archives

For individuals, saving important emails as EML files provides a simple, future-proof backup:

Download receipts, booking confirmations, and important correspondence
Store them in cloud storage (Google Drive, Dropbox, etc.) alongside related documents
Access them years later without depending on any specific email provider

How to Open EML Files

Using Our Free Online Viewer

The easiest way to view an EML file is with our free Online EML Viewer. Simply drag and drop your file, and it renders the email with full formatting, headers, and attachment listings — all in your browser.

Key advantages of our EML Viewer:

No upload required: The file is processed entirely in your browser using JavaScript. Your email data never leaves your device.
Full rendering: See the email exactly as it would appear in an email client, with HTML formatting, images, and styling
Header inspection: View all email headers including authentication results, routing information, and technical metadata
Attachment listing: See all attachments with their names, sizes, and MIME types
Mobile friendly: Works on phones and tablets, not just desktop browsers
No account needed: No sign-up, no login — just drag, drop, and view

Using Desktop Email Clients

Most modern email clients can open EML files natively:

Mozilla Thunderbird: Double-click the EML file, or drag it into Thunderbird. Thunderbird has excellent EML support and is available on Windows, macOS, and Linux.
Microsoft Outlook: Drag the EML file into Outlook, or use File > Open & Export > Open Outlook Data File. Note that Outlook sometimes has rendering differences compared to other clients.
Apple Mail: Double-click the EML file or drag it into the Mail app. macOS handles EML files natively.
Windows Mail: On Windows 10/11, double-clicking an EML file should open it in the default Mail app.
Gmail: You can't directly open an EML file in Gmail's web interface, but you can forward it as an attachment to your Gmail address, or use our EML Viewer for quick viewing.

Using Text Editors

Since EML files are plain text, you can open them in any text editor to see the raw email content:

VS Code: Great for technical analysis — syntax highlighting makes headers easier to read
Notepad++ (Windows): Handles large EML files well
Sublime Text: Fast and lightweight for quick inspection
nano/vim (Linux/macOS): Command-line options for server environments

This approach is useful when you need to inspect raw headers, debug email authentication issues, or extract specific information programmatically. However, it won't render the HTML content — you'll see the raw HTML tags instead.

Using Command-Line Tools

For advanced users and automation workflows:

# View headers only
grep -E "^(From|To|Subject|Date):" email.eml

# Extract the subject line
grep "^Subject:" email.eml

# Count attachments
grep -c "Content-Disposition: attachment" email.eml

How to Create EML Files

You might need to save an email as an EML file for archiving or sharing. Here's how in different email clients:

Thunderbird: Right-click the email > Save As > ensure the format is EML
Outlook: Drag the email from Outlook to a folder on your desktop, or use File > Save As > change the type to "Outlook Message Format - Unicode (.msg)" isn't what you want — choose "Text Only (.txt)" and rename to .eml, or use a plugin
Apple Mail: Drag the email from Mail to your desktop — it saves as .eml by default
Gmail: Open the email > click the three dots menu (⋮) > "Download message" — this saves the email as an EML file

Security Considerations When Opening EML Files

EML files from unknown sources should be treated with the same caution as any email from an untrusted sender — perhaps even more so, since they may have been specifically crafted to exploit vulnerabilities.

Safety Guidelines

Don't click links in the email until you've verified the sender and the link destinations. Hover over links to see where they actually point.
Don't open attachments extracted from suspicious EML files. Attachments in EML files can contain malware just like attachments in regular emails.
Check email headers for signs of spoofing. Look at the Received headers, SPF/DKIM/DMARC results, and the Return-Path for inconsistencies.
Use our EML Viewer for safe viewing — it renders emails in a sandboxed environment without executing any scripts, loading external images from tracking pixels, or activating embedded content.
Scan attachments with antivirus software before opening them.
Be wary of urgency — phishing emails often create artificial time pressure ("Your account will be closed in 24 hours!").

Common Red Flags in EML Files

When analyzing an EML file for potential phishing or fraud:

Mismatched "From" header and "Return-Path": The display name says "Your Bank" but the actual address is something like random@malicious-domain.com
Failed authentication: SPF, DKIM, or DMARC failures in the headers suggest the email may be spoofed
Suspicious links: Links that use URL shorteners, look-alike domains (paypa1.com vs paypal.com), or IP addresses instead of domain names
Encoded or obfuscated content: HTML that uses excessive encoding or JavaScript to hide its true content

For a deeper understanding of email authentication, check out our guide on SPF, DKIM, and DMARC.

Frequently Asked Questions About EML Files

Can I convert an EML file to PDF? Yes. Open the EML file in an email client or our EML Viewer, then use your browser's or system's Print > Save as PDF function.

Are EML files safe to store? Yes. EML files are plain text and don't execute code on their own. The risk comes from opening links or attachments within them, not from the file itself.

How large can an EML file be? There's no technical limit, but files with large attachments can be several hundred MB. Most EML files for typical emails are between 10 KB and 10 MB.

Can I edit an EML file? Since EML files are plain text, you can edit them in any text editor. However, modifying an email after the fact will invalidate its DKIM signature, which may be important if you need to prove the email's authenticity.

What's the difference between .eml and .msg files? EML is a universal, text-based standard (RFC 5322). MSG is Microsoft Outlook's proprietary binary format. EML files work everywhere; MSG files work best in Outlook.

EML Viewer — Open and read EML files online, securely in your browser
MBOX Viewer — View MBOX mailbox archive files containing multiple emails
DMARC Analyzer — Analyze email authentication reports to understand SPF, DKIM, and DMARC results
DNS Checker — Verify your domain's DNS records, including email authentication records
iCal Viewer — View calendar invitation files often found as email attachments

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