Is it safe to open an MSG file?

Generally yes, the same as any email, but unexpected .msg attachments from unknown senders should be treated with the same caution as any email attachment.

Why did I receive a file I can't open?

This usually happens when someone forwards or exports an email as an attachment from Outlook, producing a .msg file for the recipient even if they don't use Outlook.

Definition

What is an MSG file?

Q: Can I convert an MSG file to another format?

Yes, MSG files are commonly converted to PDF for universal viewing or to EML for use in other email clients.

An MSG file (.msg) is Microsoft Outlook's proprietary format for storing a single email message — including its headers, body, and any attachments — as one self-contained file. It's built on Microsoft's older Compound File Binary format, which is why it can't be opened as plain text and generally requires Outlook or a compatible tool to read.

MSG file technical specifications

MIME type	application/vnd.ms-outlook
Underlying format	OLE2 / Compound File Binary (CFB)
File signature (hex)	D0 CF 11 E0 A1 B1 1A E1
Access method	MAPI (Messaging API)

MSG vs. EML at a glance

Working with EML files? See the EML to PDF converter or read the full MSG vs. EML breakdown.

	MSG	EML
Created by	Microsoft Outlook	Most other email clients
Format type	Proprietary binary	Open standard (RFC 5322)
Human-readable as text	No	Yes
Needs Outlook to open natively	Usually	No

What's actually inside one

An MSG file is a compound document — the same underlying container format Microsoft historically used for legacy .doc and .xls files. Rather than storing plain text, it packages several distinct pieces into one binary file:

Header data — sender, recipients, subject line, and timestamp
Message body — the email text, often stored in more than one format (plain text, HTML, and RTF) simultaneously
Attachments — embedded directly inside the same file, rather than referenced separately
Outlook-specific properties — flags, categories, importance level, and other metadata Outlook uses internally (MAPI properties)

That last point is the key difference from most other email formats: an MSG file carries Outlook's internal bookkeeping along with the message itself, which is part of why it's proprietary rather than an open standard.

How to open an MSG file

In Microsoft Outlook — double-clicking a .msg file opens it directly if Outlook is installed on your device.
On a device without Outlook — Mac, Linux, and mobile users generally can't open .msg files natively, since Outlook isn't required (or in some cases available) on those platforms.
Convert it to a universal format — turning the .msg file into a PDF makes it readable on any device, in any PDF viewer, without Outlook at all. See the full guide to converting MSG to PDF for all available methods.

Convert your MSG file to PDF →

Frequently asked questions

Not natively, since Outlook for Mac doesn't handle .msg files the same way Windows Outlook does. Converting the file to PDF is the most reliable way to view it on a Mac.

Generally yes, the same as any email — but treat unexpected .msg attachments from unknown senders with the same caution you would any email attachment.

Yes — MSG files are commonly converted to PDF for universal viewing, or to EML for use in other email clients.

This usually happens when someone forwards or exports an email as an attachment from Outlook — the recipient gets a .msg file even if they don't use Outlook themselves. Converting it to PDF is the quickest way to open it on any device.