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.
How to open 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
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.
.msg file signature (magic bytes)
Programs recognise a .msg file by the bytes at the start of the file, not by its name. These are the signatures for MSG. For a full breakdown, see the MSG file signature page.
| Hex signature | Offset | 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
Details on this page were checked against authoritative references: