What Is .eml

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Last updated: April 10, 2026

Quick Answer: .eml is an Electronic Mail format standardized under RFC 2822 in 2001, used to store complete email messages including headers, body, and attachments in a single plain-text file. With billions of files existing across enterprise and personal systems globally, .eml remains the most universally compatible email format supported by virtually all email clients including Outlook, Gmail, and Thunderbird. The format ensures long-term accessibility and portability since it uses open standards and can be opened in any text editor.

Key Facts

RFC 2822 standard established in 2001 as the foundation for .eml and email message formatting
Each .eml file stores a complete email with all headers, body text, and attachments in a single self-contained file
Supported natively by all major email clients including Microsoft Outlook, Gmail, Mozilla Thunderbird, and Apple Mail
Plain-text format allows .eml files to be opened in any text editor on Windows, macOS, and Linux without proprietary software
Billions of .eml files stored across enterprise email systems, personal archives, and cloud backup services worldwide

Overview

.eml stands for Electronic Mail, a standardized file format used to store complete email messages in a single, portable file. Developed based on RFC 2822 standards established in 2001, the .eml format has become the de facto standard for email storage and interchange across the internet. Each .eml file contains a fully self-contained email message, including headers, body text, and all attachments, making it universally compatible across email platforms and operating systems.

The .eml format was designed to solve the challenge of email portability in an era when email clients varied widely in their proprietary storage methods. By creating a plain-text, standards-based format, developers ensured that email messages could be easily transferred between different email clients, archived for long-term storage, and accessed using simple text editors if necessary. Today, .eml remains the most widely supported email file format, with billions of files stored across enterprise systems, personal archives, and cloud services worldwide.

How It Works

.eml files function as plain-text containers that follow a specific structural format defined by email standards. When an email client exports a message as .eml, it captures the complete email including all headers, the message body, and any attachments, storing everything in a single file.

Headers Section: The .eml file begins with email headers that contain metadata like sender address, recipient addresses, subject line, date, and time. These headers follow a key-value format (e.g., "From: [email protected]") and provide essential routing and identification information that was used when the email traveled through mail servers.
Body Content: Following the headers is a blank line, then the email body containing the actual message text. The body can be plain text or formatted HTML, and the .eml format preserves all original formatting, fonts, and styling exactly as it appeared in the original email client.
MIME Encoding: When .eml files contain attachments or non-ASCII characters, they use MIME (Multipurpose Internet Mail Extensions) encoding to represent binary data as text. This allows attachments like images, PDFs, or documents to be embedded directly within the text-based .eml file without corruption.
Attachment Storage: Attachments in .eml files are encoded using Base64, a method that converts binary data into text format. When you open an .eml file in an email client, the application automatically decodes these attachments, allowing you to view and extract them just as you would in the original email.
Standalone File Format: Unlike some email formats that require a database or container file, each .eml file is completely independent and self-contained. This means you can move, copy, or share individual .eml files without needing any companion files or databases.

Key Comparisons

Format	File Type	Compatibility	Best For
.eml	Plain text, single email	Universal across all platforms and clients	Individual email export, archiving, sharing
.msg	Binary, Microsoft proprietary	Primarily Outlook, limited third-party support	Outlook-specific storage and collaboration
.pst	Binary, Microsoft database container	Outlook primary, some migration tools available	Multi-email archive, folder structure storage
.mbox	Plain text, multiple emails in one file	Common in Unix/Linux systems, email migration	Bulk email archiving, server-side storage

Why It Matters

Universal Accessibility: Because .eml is plain text and standards-based, you can open and read .eml files in virtually any text editor on Windows, macOS, or Linux without requiring proprietary software. This ensures your emails remain accessible even if the original email client becomes obsolete or unavailable.
Email Migration: When switching from one email client to another, .eml format makes migration straightforward. Gmail, Outlook, Thunderbird, Apple Mail, and dozens of other clients all support importing .eml files, eliminating vendor lock-in and making it simple to change email platforms.
Long-term Archiving: Organizations and individuals use .eml format for legal compliance and historical record-keeping. Because the format is non-proprietary and text-based, .eml files can be reliably preserved and accessed for decades without worrying about software compatibility issues.
Security and Privacy: The plain-text nature of .eml allows for easy encryption, backup, and secure transmission. You can encrypt individual .eml files, back them up to external drives or cloud storage, and share them securely knowing exactly what data you're transmitting.
Integration and Automation: Developers and system administrators can easily parse, process, and integrate .eml files into custom applications and workflows because the format is based on open standards. This enables sophisticated email automation, filtering, and processing systems that would be difficult with proprietary formats.

The .eml format continues to be essential in modern email infrastructure despite competition from cloud-based systems and proprietary platforms. Its simplicity, portability, and universal support make it the standard choice for email interchange, archiving, and personal data control, ensuring that your email messages can be accessed and used on your terms for years to come.