What is a .msg file?
Outlook Message · Data · Microsoft · 1997
MSG is Outlook's native format for a single saved email, contact, or other item. Unlike the plain-text EML used elsewhere, a MSG is a binary OLE2 compound file, Outlook's structured container for that item's properties, body and attachments.
What is a .msg file used for?
A MSG file is a single email, contact, appointment or other Outlook item saved to disk, produced whenever you drag a message out of Outlook or use its Save As dialog.
Under the hood it is a Compound File Binary Format file (the same OLE2 container as an old .doc), storing the message's properties, headers, body and attachments as separate internal streams rather than as plain text.
That structure is documented in Microsoft's own MS-OXMSG specification, so third-party libraries can read a MSG without Outlook, which is how many email-migration and archiving tools support it.
Because it is Outlook-specific, a MSG is less portable than the plain-text EML format; converting between the two is a common step when moving mail out of Outlook to another client.
What opens a .msg file?
The .msg format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Outlook
- Windows Mail (limited)
macOS
- Outlook for Mac
Linux
- Not natively; convert to EML first
Web
- Not applicable
Open a .msg file step by step
- Confirm the file really is a .msg. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Outlook or Windows Mail (limited).
- On Mac, use Outlook for Mac.
- On Linux, try Not natively; convert to EML first.
- Still stuck? Convert the .msg to EML, which opens more widely.
Why can't I open my .msg file?
Almost always because no installed app understands MSG. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .msg at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .msg file
You can convert a .msg file to EML, PDF using a conversion tool or the export menu of an app that opens it.
What is the .msg file signature (magic bytes)?
A .msg file starts with the hex bytes D0 CF 11 E0 A1 B1 1A E1. Programs identify MSG by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for MSG. For a full breakdown, see the OLE2 Compound File file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| D0 CF 11 E0 A1 B1 1A E1 | 0 | - | OLE2 compound file, shared with legacy Office .doc/.xls/.ppt and .msi |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .msg file?
MSG is Outlook's native format for a single saved email, contact, or other item. Unlike the plain-text EML used elsewhere, a MSG is a binary OLE2 compound file, Outlook's structured container for that item's properties, body and attachments.
How do I open a MSG file without Outlook?
Outlook for Mac also opens it. Without any version of Outlook, use a dedicated MSG viewer or converter, since the format's OLE2 structure needs a tool that specifically understands it, unlike the plain-text EML.
How do I convert MSG to EML?
Open it in Outlook and use Save As, choosing a plain-text or EML-compatible option if offered, or use a dedicated MSG-to-EML converter. Many email migration tools handle this conversion automatically.
Related formats
Sources
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