What Is an EML File? How to Open, Read, and Convert It

What Is an EML File?

An EML file is a standard email message file. The .eml extension stands for Electronic Mail and follows the RFC 2822 format — the same standard used to transmit emails across the internet. Each EML file contains exactly one email message: the headers (From, To, Subject, Date), the message body, and any attachments.

EML files are created by virtually every email client when you export or save individual messages:

• Microsoft Outlook can save messages as .eml via File > Save As
• Thunderbird uses EML as its native individual message format
• Apple Mail saves messages as .eml when dragged out of the application
• Windows Mail creates EML files for exported messages
• Gmail supports EML export through Google Takeout

Because EML follows an open standard, a file created in Outlook can be opened in Thunderbird, Apple Mail, or any other standards-compliant email client — making it the most universally compatible individual email format.

What Is Inside an EML File?

An EML file is a plain text file with a specific structure. You can open one in any text editor to see its raw contents:

From: sender@example.com
To: recipient@example.com
Subject: Meeting tomorrow
Date: Mon, 09 Jun 2026 10:30:00 +0000
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="boundary_string"

--boundary_string
Content-Type: text/plain; charset="utf-8"

Hello, let's meet tomorrow at 3pm.

--boundary_string
Content-Type: application/pdf; name="agenda.pdf"
Content-Disposition: attachment; filename="agenda.pdf"
Content-Transfer-Encoding: base64

[base64 encoded attachment data]

Key sections of an EML file:

• Headers — metadata including sender, recipient, subject, date, MIME version, and message ID
• Body — the message text in plain text and/or HTML
• Attachments — encoded as MIME parts with base64 encoding
• Inline images — embedded graphics, also encoded as MIME parts

The entire message is self-contained in a single file. Nothing is stored externally.

EML vs Other Email Formats

Format	Contains	Compatible with	Best for
EML	One message	All email clients	Sharing individual emails
MSG	One message	Outlook only (natively)	Microsoft ecosystem
PST	Entire mailbox	Outlook	Outlook archiving
MBOX	Multiple messages	Thunderbird, Apple Mail	Open-source clients
EMLX	One message + metadata	Apple Mail only	macOS archiving

EML is the most portable of the single-message formats. MSG files require Outlook or a dedicated viewer to open natively; EML files open everywhere.

For a detailed comparison of MSG and EML, see MSG vs EML: Key Differences.

How to Open an EML File

On Windows

Method 1: Double-click On Windows 10 and 11, double-clicking an EML file opens it in the default Mail app. If no association is set, right-click > Open with > Mail.

Method 2: Drag into Outlook Drag the EML file directly into an open Outlook folder. Outlook will import it as a regular message.

Method 3: Thunderbird Install Thunderbird (free) and drag the EML file into any folder. Thunderbird reads EML natively.

On macOS

Method 1: Double-click Apple Mail is the default handler for EML files on macOS. Double-clicking opens the message directly.

Method 2: Drag into Apple Mail Drag the EML file into an Apple Mail folder to import it permanently.

On Linux

Thunderbird reads EML files natively — just drag and drop. Evolution and KMail also support EML.

For command-line access, EML files are plain text and can be read with any text viewer:

cat message.eml
less message.eml

Online

Upload the EML file to MailtoPst to view its contents online without installing any software. You can also convert it to PST, MBOX, or MSG from the same interface.

How to Convert EML Files

EML to PST

If you need to open EML files in Microsoft Outlook, converting to PST is the standard approach. The EML to PST converter bundles individual EML messages into a single Outlook-compatible PST archive, preserving folder structure, metadata, and attachments.

EML to MBOX

To import EML messages into Thunderbird or Apple Mail as a bulk archive, convert to MBOX format using the EML to MBOX converter. The resulting MBOX file can be imported directly into either client.

EML to MSG

If you need to share EML messages with colleagues who use Outlook and prefer the MSG format, use the EML to MSG converter. MSG files retain full Outlook-specific formatting and properties.

Batch Conversion

MailtoPst supports batch EML conversion — upload a folder of EML files and convert them all at once to your target format. This is particularly useful when migrating email archives or preparing messages for eDiscovery platforms.

Common EML File Problems

EML File Won’t Open

If double-clicking an EML file does nothing:

1. Right-click the file and choose “Open with”
2. Select Thunderbird, Mail, or Outlook
3. To make the association permanent, check “Always use this app”

EML File Shows Garbled Characters

This usually means a character encoding mismatch. Most email clients handle this automatically, but if you see strange characters, try opening the EML in Thunderbird, which has robust encoding detection.

EML Attachments Not Showing

Some email clients hide MIME-encoded attachments. Try opening the EML in Thunderbird or converting it to MSG format, which handles attachment display more reliably in Outlook.

Large EML Files

Very large EML files (>100 MB) often contain multiple large attachments encoded in base64. Opening them in Thunderbird or converting with MailtoPst are both reliable options.

EML Files in eDiscovery and Compliance

EML is one of the most common formats in legal discovery and regulatory compliance. Because each EML file contains exactly one email with all its metadata, it is ideal for:

• Document production — individual messages can be bates-numbered and reviewed
• Evidence preservation — self-contained files are easy to authenticate
• Review platforms — most eDiscovery tools (Relativity, Nuix, Concordance) natively ingest EML
• Long-term archiving — open standard with no vendor lock-in

For organizations receiving PST archives in discovery, converting to EML provides individual message access without requiring Outlook deployment to every reviewer. See our eDiscovery use case for more.

Key Takeaways

• EML files contain a single email message following the open RFC 2822 standard
• They open natively in almost every email client: Outlook, Thunderbird, Apple Mail, Windows Mail
• EML is more portable than MSG (Outlook-only) and more granular than PST or MBOX (multi-message)
• Convert EML to PST with MailtoPst to open archives in Outlook, or to MBOX for Thunderbird/Apple Mail

Convert EML files now →