.eml vs .msg: What's the Difference?

Both hold a single email. The difference is who can read it.

.eml is an open standard. Plain text, defined by the same internet specification that governs how email moves between servers. Practically every mail program can open one, on any operating system.

.msg is Microsoft's proprietary format. A binary file produced by Outlook, storing not just the message but Outlook's own internal properties. Outside the Microsoft ecosystem, support is patchy at best.

If you're deciding how to save something, that sentence is usually the whole answer: choose .eml unless you specifically need Outlook-only data preserved.

Open an .eml file here — in your browser, nothing uploaded.

Side by side

What each one actually stores

An .eml file is a transcript of the message as it was transmitted: headers at the top, a blank line, then the body and any attachments encoded as text. Because that's exactly what travels between mail servers, nothing has to be translated to produce the file. Open it in Notepad and you can read the headers yourself.

A .msg file is a database record. Outlook writes out its internal representation of the item, including MAPI properties — the metadata Outlook uses to track things the standard email format has no concept of. That's the format's real advantage: it can hold a follow-up flag, a category colour, a task due date, or the details of a meeting invitation, none of which survive a conversion to .eml.

It's also why .msg files aren't readable outside Outlook. The structure is a Microsoft compound file, not text.

Which to use

Use .eml when:

• Someone else needs to open it and you don't know what they use
• You're archiving for the long term, where format lock-in is a genuine risk
• The message may be needed as evidence — .eml preserves the full routing headers in a form anyone can verify
• You're migrating between providers
• You want to be able to read the file without special software in ten years

Use .msg when:

• You're staying inside Outlook and want its flags, categories, or task data preserved
• You're saving a calendar invitation or meeting request with all its properties
• Your organisation's process specifically requires it

For most people, most of the time, .eml is the safer default. A format you can read in Notepad will outlive a format that needs a specific commercial product.

Converting between them

.msg to .eml: In Outlook, open the message and use Save As, choosing the plain-text-based option where offered. You'll lose Outlook-specific properties in the process — that's inherent to the conversion, not a bug in the tool you use. Dragging a message from Outlook directly into a folder in Windows Explorer produces .msg, so Save As is the step that matters.

.eml to .msg: Open the .eml in Outlook, then save it. Outlook will write out its own format.

Either one to PDF: the usual reason people ask this question. Open the message and print to PDF, which keeps the text selectable and searchable rather than producing a screenshot. Full walkthrough here.

A word of caution about the many online converters for this: they require you to upload the email to someone else's server. For a marketing newsletter that's fine. For anything involving a client, a contract, medical information, or a legal matter, it means handing a confidential document to a third party whose retention policy you haven't read. A tool that works locally in your browser avoids the question entirely.

Which one is better for evidence?

.eml, in most circumstances — not because it holds more, but because it's verifiable. The full Received header chain is present and readable by anyone with a text editor, which means the other side can check it without trusting your software. A .msg file carries the same routing data, but reading it requires Outlook or a converter, which introduces a step someone can dispute.

Whichever you use: keep the original file. A screenshot or a forwarded copy loses the headers, and the headers are the part that carries proof.

Common questions

Can Outlook open .eml files? Yes. Outlook reads both, even though it writes .msg by default.

Can Thunderbird open .msg files? Not natively. You'll need a converter, or access to Outlook.

Is .eml the same as .mbox? No. One .eml is one message. An .mbox file holds an entire folder of messages.

Why is my .msg file smaller? .eml encodes attachments as base64 text, which adds roughly a third to their size. .msg stores them as binary.

Can I read a .msg file in a text editor? Not usefully. It's binary — you'll see fragments of text surrounded by unreadable characters.

Open an .eml file in your browser — free, nothing installed, nothing uploaded.