EML vs MSG: The Difference, How to Open Each, and How to Convert Them

Last updated July 2026.

Quick answer: The difference between EML and MSG is that EML is an open standard, storing one email as plain MIME text that almost any program can read, while MSG is Microsoft Outlook's proprietary binary format that preserves Outlook-specific data such as categories and flags. Both hold a single message. Choose EML for archiving and cross-platform work, and MSG only when you need Outlook metadata to survive an Outlook-to-Outlook move.

Sooner or later, anyone who works with email at scale ends up holding a pile of files with .eml or .msg extensions. Maybe you exported a mailbox, maybe a colleague forwarded an archive, maybe a system dumped them for you. They look like emails, they smell like emails, but double-clicking one doesn't always do what you expect, and getting the data out of them is its own small adventure. Let's clear it up.

EML vs MSG file format: the comparison table

What Is an .eml File?

An .eml file is a single email message saved in the standard MIME format defined by internet RFCs. It's essentially the raw email exactly as it traveled across the network: a block of headers (From, To, Subject, Date, and dozens of technical ones) followed by the body and any attachments, all encoded as plain text. Because it's an open standard, .eml is portable: Apple Mail, Thunderbird, Gmail, and most clients can open it, and any text editor will show you the raw guts if you're curious.

That openness is why .eml is the friendliest format for extraction. The structure is documented, predictable, and not tied to any one vendor.

What Is an .msg File?

An .msg file is Microsoft Outlook's proprietary format. It also stores a single message (headers, body, attachments), but it does so in a binary container (the same "compound file" structure Office uses elsewhere) rather than plain text. The upside is that it preserves Outlook-specific richness like categories, flags, and certain rich-text quirks. The downside is that it's a Microsoft format, so opening it cleanly outside the Microsoft ecosystem can be hit or miss.

Practically speaking: if you're inside Outlook on Windows, .msg files just work. Anywhere else, expect a little friction.

.eml vs .msg: The Short Version

• Standard vs proprietary: .eml is an open MIME standard; .msg is Outlook's own format.
• Storage: .eml is human-readable text; .msg is a binary container.
• Portability: .eml opens almost anywhere; .msg is happiest in Outlook.
• Extra metadata: .msg can carry Outlook-specific fields that .eml doesn't.

Neither is "better", they're just built for different worlds. The format only really matters when you need to do something with the contents, which is usually the whole point.

How to Open Each Format

For .eml: double-click and most desktop mail clients will render it. To see the raw structure, open it in any text editor, you'll see the headers at the top and the encoded body below. That rawness is a feature when you're debugging or extracting.

For .msg: on Windows with Outlook installed, double-clicking opens it natively. Without Outlook, you'll need a viewer app or a conversion tool, because the binary format won't render as text. This is the moment most people discover their .msg files are stuck.

Converting Emails to CSV or Excel

Opening a file lets you read one email. The real task is usually turning a folder full of them into a spreadsheet: rows of senders, dates, subjects, and the specific fields you care about. Doing that by hand means opening each message, copying values, and pasting them into Excel, which is slow and error-prone regardless of whether the source is .eml or .msg.

The faster path is a parser that reads both formats and handles the encoding details for you. With MailParse, you drop in your .eml or .msg files, or paste raw email text if that's what you have, and it extracts the standard headers automatically: sender, recipients, date, subject, body, and a list of attachments. You pick the output you want, whether that's CSV for a quick import, XLSX for a polished sheet, or JSON for a downstream system.

A few things that make this painless in practice:

• Both formats, one workflow: .eml and .msg go through the same pipeline, so you don't have to sort your files first.
• Bulk upload: drop a whole folder and get one combined spreadsheet out instead of one file at a time.
• Custom fields: if you need an invoice number or order ID that lives inside the body, define it once and pull it from every message.
• No encoding headaches: quoted-printable, base64, and multipart bodies are decoded for you, so you don't see =20 and gibberish in your cells.

Can Outlook open EML files?

Yes. Outlook opens .eml files and can import them, even though its own single-message format is .msg. Double-click an .eml on a Windows machine with Outlook installed and it renders like any message. What Outlook will not do is preserve its own private properties when you save that message back out as .eml, because the standard has nowhere to put a category or a follow-up flag.

How do I convert MSG to EML?

The reliable route is to open the .msg in Outlook and save or drag the message out as .eml, which forces Outlook to write standards-compliant MIME. Bulk jobs need a converter, since doing this by hand across a few hundred files is a lost afternoon. Expect to lose the Outlook-only properties in the process: flags, categories, and custom MAPI fields have no equivalent in the EML standard, so they are dropped rather than translated.

Which is better for archiving, EML or MSG?

EML, in almost every case. An archive should still be readable in ten years by software nobody has written yet, and a plain text MIME file satisfies that in a way a proprietary binary container does not. EML is also trivially greppable, which matters enormously during e-discovery or an audit. Keep MSG only when the Outlook metadata is itself part of the record you must preserve.

Do EML and MSG files contain attachments?

Both do. An .eml carries its attachments inline as base64 encoded text, which is why a message with a 4 MB PDF becomes a roughly 5.5 MB file. An .msg stores attachments as separate streams inside its binary container. In both cases the attachment travels with the message, so a single file is the complete email, and neither format depends on a mail server to be readable.

What is EML and MSG in Outlook?

Inside Outlook, .msg is the native format used when you save or drag a message to disk, and .eml is the interchange format Outlook can read and write for compatibility with everything else. Practically, Outlook treats .msg as its own and .eml as a guest it accommodates politely. If you are exporting mail for anyone outside your organization, export .eml.

Can people open an MSG or EML file?

Most people can open an .eml file, and many cannot open an .msg file. EML is plain MIME text, so Apple Mail, Thunderbird, Gmail, and most webmail clients open it without any extra software. MSG is Outlook's binary format, so a recipient without Outlook on Windows usually sees an unreadable file or is prompted to find an app. If you are sending a saved email to someone whose setup you do not know, send .eml.

This is the practical reason the two formats matter at all. The file you choose decides whether the person on the other end reads the message or emails you back asking what to do with it. Mac users in particular hit this constantly, because macOS has no native handler for .msg.

What does EML and MSG mean for downloads?

When a web app or mail client offers to download a message, EML gives you a portable copy that opens almost anywhere, and MSG gives you an Outlook-native copy that keeps Outlook-specific properties such as categories, flags, and follow-up state. Both download a single complete message including its attachments. Pick EML unless the file is going straight back into Outlook.

For bulk downloads the choice matters more than it looks. A folder of a few thousand .eml files can be read by almost any script or parser, while the same folder in .msg form needs a tool that understands Outlook's compound binary structure. That difference decides how much work it is later to convert the whole batch to a spreadsheet.

The Bottom Line

If your files are .eml, you've got the portable, standards-based format and you're in good shape. If they're .msg, you've got Outlook's format and you'll want a tool that reads it without forcing you back into Outlook. Either way, the format is just the container: what you actually want is the data inside it, laid out in clean columns. For a deeper look at the standard itself, read what an EML file is and what it contains, or the companion explainer on what a MSG file is. Then send your files through the EML to CSV converter or the MSG to Excel converter, or browse the use cases to see how teams handle invoices, orders, and leads the same way.