Updated October 2026
You've been sent a .msg file — usually because someone forwarded an email as an attachment from Outlook — and you don't have Outlook installed, or don't want to install it just to read one message. Here are the actual options, and why most of them are more complicated than they should be.
A .msg file isn't a plain-text email format like .eml — it's Microsoft's proprietary CFBF (Compound File Binary Format) container, the same binary format historically used by old .doc and .xls files, packed with binary MAPI property streams that encode the sender, recipients, body, and attachments. That format is undocumented outside Microsoft's own code, which is exactly why most non-Outlook email clients — Mac Mail, Gmail's web interface, Thunderbird — simply refuse to open a .msg attachment. See the CFBF format explainer for the technical detail.
This tool uses msgreader, an open-source, community-reverse-engineered CFBF/MAPI parser, running entirely in your browser via JavaScript. Drag and drop (or click to choose) your .msg file, and it immediately shows the sender, recipients, subject, date, body text, and a list of attachments you can download individually. Nothing is uploaded — the file is read locally using the browser's File API and handed directly to the in-page parser. This is the fastest option if you just need to read one message once, on any operating system, without installing anything.
If you have (or can create) a free Microsoft/Outlook.com account, Outlook on the web can open .msg attachments uploaded through its interface, since it's the same Microsoft codebase that defines the format. This requires an account and an internet connection, and means uploading the file to Microsoft's servers — a meaningful difference from a purely local, offline tool if privacy or confidentiality of the message content matters (see the next section).
Various third-party desktop applications (particularly on Windows) can open .msg files without a full Outlook license. These typically require a download and install, and quality/maintenance varies a lot between them — if you only need to open an occasional single file, the install overhead often isn't worth it compared to a browser-based option.
A common piece of bad advice: renaming a .msg file's extension to .eml and opening it as a plain email. This doesn't work because the two formats are structurally different at the byte level — .eml is a plain-text MIME format, while .msg is the binary CFBF container described above. Changing the file extension doesn't change the actual bytes inside the file, so an .eml-aware reader will simply fail to parse a renamed .msg file (or vice versa). See the .msg vs .eml comparison for the full breakdown.
For a one-off read of a single .msg file — especially on a Mac, Linux machine, or anywhere you don't already have an Outlook license — a local, browser-based viewer that doesn't require an account or upload is generally the fastest and most private option. Reach for Outlook on the web if you already have a Microsoft account and don't mind uploading the file; reach for a desktop application only if you're processing many .msg files regularly and want a permanent local tool.
Will this work on an iPhone or Android device? Any modern mobile browser supports the same File API and JavaScript this tool relies on, so yes — though attaching/selecting a .msg file from a phone's file system depends on how it was originally saved to the device.
Does this tool need an internet connection to work? Only to load the page itself the first time. After that initial load, parsing happens entirely locally and the page works offline — there's no server round-trip involved in reading a file.
What if the file won't open in any of these options? It may be corrupted, not actually a .msg/CFBF file despite the extension, or an unusual variant an open-source parser doesn't cover. See the FAQ on the main tool page for troubleshooting.