How to Open Email Files: A Complete Guide to .EML, .MSG, and Other Email Formats

Email files come in several formats, and knowing which format you're dealing with — and what tools can open it — makes all the difference. Whether you've received an archived email, downloaded an attachment, or exported messages from an old account, this guide explains exactly what email files are, how they work, and what factors shape how you'll open them.

What Are Email Files?

When an email is saved to disk rather than stored on a mail server, it becomes a standalone file on your computer. These files preserve the message content, headers, timestamps, and often attachments — essentially a snapshot of the email outside of any email client.

The most common formats are:

Understanding which format you have is the first step — because no single tool opens all of them.

How to Open .EML Files

.EML is an open, text-based format following the MIME standard, which makes it the most universally supported email file type.

Options for opening .EML files:

• Microsoft Outlook — Double-clicking an .eml file will typically open it directly if Outlook is installed and set as the default mail client.
• Mozilla Thunderbird — Supports .eml natively. You can drag and drop the file into a Thunderbird folder, or use the ImportExportTools NG add-on for bulk imports.
• Apple Mail (macOS) — Double-clicking an .eml file usually opens it without any extra steps.
• Windows Mail / Mail app — On Windows 10 and 11, the built-in Mail app can open .eml files directly.
• Text editor — Because .eml files are plain text (MIME-encoded), you can open them in Notepad or any text editor to read raw headers and body content, though attachments will appear as Base64-encoded strings.

How to Open .MSG Files

.MSG is a proprietary Microsoft format. It stores richer data than .eml — including formatting, embedded objects, and metadata — but this comes at the cost of compatibility.

• Microsoft Outlook is the primary tool designed to open .msg files natively. If Outlook is installed, double-clicking the file works immediately.
• Outlook Viewer (free from Microsoft) allows you to view .msg files without a full Outlook installation, though editing isn't supported.
• On macOS or Linux, .msg support is limited. Tools like MSGViewer (open source) or third-party converters can extract readable content, but formatting may not render perfectly.
• Web-based viewers exist for one-off access — useful if you occasionally receive .msg files but don't use Outlook.

How to Open .MBOX Files 📬

.MBOX is a container format that holds multiple emails in a single file, each stored sequentially. It's commonly produced by Gmail Takeout exports and legacy Unix mail systems.

• Mozilla Thunderbird with the ImportExportTools NG add-on handles .mbox files reliably.
• Apple Mail can import .mbox files through the File > Import Mailboxes menu.
• Gmail does not import .mbox directly through the web interface — you'd typically need a desktop client or a dedicated migration tool.
• Text editors can technically open .mbox files, but parsing individual messages manually is impractical for anything beyond a handful of emails.

How to Open .PST and .OST Files

.PST (Personal Storage Table) and .OST (Offline Storage Table) files are Outlook's personal archive formats, often large and containing thousands of messages, contacts, and calendar entries.

• Microsoft Outlook opens .pst files natively via File > Open & Export > Open Outlook Data File.
• .OST files are tied to specific accounts and are harder to open independently — they're meant to sync with an Exchange or Microsoft 365 account, not to be portable backups.
• Third-party tools exist for reading .pst files without Outlook, though feature depth varies widely.

Key Variables That Affect Which Approach Works

Not all situations are equal. Several factors determine which method makes the most sense: ⚙️

• Operating system — Windows, macOS, and Linux have different levels of native support for each format. .msg files, for example, are far easier to open on Windows than macOS.
• Whether you have a licensed email client — Outlook opens .msg and .pst files cleanly, but it's a paid application. Free alternatives cover .eml and .mbox well, but have real limitations with proprietary Microsoft formats.
• File volume — Opening one .eml file is trivial. Importing thousands of .mbox messages into a usable mail archive is a different task requiring a more deliberate approach.
• What you need to do with the file — Read-only viewing has more tool options than searching, replying, or extracting attachments at scale.
• Technical comfort level — Command-line tools and open-source options often provide the most flexibility but require more setup than graphical applications.

When Compatibility Gets Complicated 🔍

Format mismatches are a common source of frustration. An .eml file saved by Thunderbird on Linux will open in Apple Mail on macOS without issue. A .msg file created by a corporate Outlook installation may render incorrectly — or not at all — on a device without Microsoft Office.

Conversion is often the practical solution. Tools exist to convert .msg to .eml, .pst to .mbox, or other formats, letting you move between ecosystems. The fidelity of these conversions varies — rich formatting, embedded images, and complex attachments are the most likely to degrade.

The right approach for you depends on what format you have, what software is already installed on your system, how many files you're dealing with, and what you ultimately need to do with the messages. Those specifics — your setup, your volume, and your end goal — are what determine whether a simple double-click solves the problem or whether a more deliberate workflow is worth setting up.