File Extension GuideWhat is a MSG File?
A MSG file is a single Outlook item saved as one file, with the .msg extension. Most often it is one email, saved with its subject, sender, recipients, date, body and any attachments all kept together.
Microsoft created the MSG format for Outlook. When you save or drag an email out of Outlook, it writes a .msg file. Because the format is built for Outlook, a MSG file can keep details that other formats drop, such as message flags, read receipts and other Outlook fields.
The trade-off is that MSG is a binary file, not plain text. You cannot read it in Notepad the way you can read an EML file. To see a MSG the normal way you use Outlook or a MSG viewer. The key idea is one item per file: each .msg holds a single email, contact, appointment or task, not a whole mailbox.
Quick Facts
| File Extension | .msg |
| Full Name | Outlook Message (Outlook Item) |
| Category | Email Message File (single Outlook item) |
| MIME Type | application/vnd.ms-outlook (de-facto) |
| Built On | Compound File Binary Format (OLE), MS-OXMSG |
| Made By | Microsoft (for Outlook) |
| File Type | Binary (not readable as plain text) |
| Character Encoding | ANSI or Unicode, stored as properties |
| Items Per File | One (a single Outlook item) |
| Attachment Support | Yes, stored inside the file |
| Typical Size | A few KB to several MB, depending on attachments |
History & Origins
The MSG file grew out of Microsoft Outlook and the way Windows stores complex files:
Early 1990s - Compound Files
Microsoft built the Compound File Binary Format, a way to keep many parts inside one file, a bit like folders and files packed into a single box. MSG is built on this design.
1997 - Outlook and .msg
Microsoft Outlook launched and used the .msg file to save a single email or item to disk. Saving or dragging a message out of Outlook created a .msg file.
2008 - Open Specification
Microsoft published the MS-OXMSG specification, a public document that explains the .msg layout. This let other programs read and write MSG files too.
Today
MSG is the standard way Outlook users save and share single emails. It also stores saved contacts, appointments and tasks as .msg files.
MSG File Structure
A MSG file is a compound file. Think of it as a small container that holds many parts inside one file. Each part is either a storage (like a folder) or a stream (like a file). The parts hold the message details, the people on the email and the attachments. Here is the idea:
+-- Property streams subject, date, body, flags
+-- Sender and recipients To, Cc, Bcc entries
+-- Attachment storages each file kept inside
+-- Named properties extra Outlook fields
Every piece of the email, from the subject line to a read receipt setting, is saved as a property. This is why a MSG file can carry Outlook details that plainer formats lose.
The Main Parts
Properties
The message details, each saved as a property: subject, date, sender, body text, importance, flags and more. Outlook reads these to show the email.
Recipients
The people on the message. Each To, Cc and Bcc entry is stored with its name and email address inside its own part of the file.
Attachments
Files sent with the email are kept inside the same .msg. An attachment can even be another email, which Outlook stores as a message within the message.
Storages and Streams
The folders and files inside the compound file. This layout lets one .msg hold text, people and attachments together in a tidy structure.
Common Details Stored in a MSG File
| Detail | What It Means | Example |
|---|---|---|
Subject | The subject line | Weekly Report |
Sender | Who sent the email | John Smith <john@example.com> |
To / Cc | Who the email was sent to | jane@example.com |
Date | When it was sent | Mon, 20 Jan 2025 09:00:00 |
Body | The message text, plain or HTML | Hi Jane, here is the report ... |
Importance | Priority flag set in Outlook | High |
Attachments | Files kept inside the message | report.pdf |
What a MSG File Can Hold
Most MSG files are saved emails, but the format can store other single Outlook items too. They all use the same .msg extension:
A Saved Message
- The most common kind
- Holds the full email
- Keeps attachments inside
A Contact Card
- A saved Outlook contact
- Name, email and phone
- Shared as one file
A Calendar Item
- A saved meeting or event
- Date, time and place
- Opens back in Outlook
A To-Do Item
- A saved Outlook task
- Title, due date and notes
- Single item in one file
How to Open a MSG File
Outlook opens MSG best, but it is not the only way. Here are your choices by system:
Windows
macOS
No Outlook
Convert and Open
Open a MSG in Microsoft Outlook
- Double-click the .msg file. If Outlook is installed, it opens the message in a normal email window.
- Read the email, with the subject, sender, date and body shown as usual.
- Save any attachments you need straight from the open message.
Open a MSG Without Outlook
- Use a MSG viewer such as the Univik MSG Viewer, which opens the file and shows the email with no Outlook needed.
- Load the .msg file in the viewer to read the message and its attachments.
- Or convert it first, turn the MSG into PDF or EML, then open it in any reader or email program.
How to Create or Save a MSG File
Outlook makes a MSG file whenever you save a single message to disk. There are two easy ways:
Save As in Outlook
- Open or select the email in Outlook.
- Go to File then Save As.
- Pick a folder and keep the type as Outlook Message Format (.msg).
- The email is saved as a .msg file.
Drag and Drop
- Open the folder or desktop where you want the file.
- Drag the email from Outlook onto that folder.
- Outlook drops a .msg copy of the message there.
- Keep the .msg file or send it on to someone else.
Common Uses
MSG files show up in many everyday Outlook tasks:
Save an Email
Keep an important Outlook email as a file on your computer, with its attachments and full details kept intact.
Share With Outlook Users
Send a saved message to a colleague who uses Outlook. They open the .msg and see it just as you did.
Attach an Email
Send one email inside another. Outlook attaches the first message as a .msg so the whole thing travels along.
Legal and Evidence
One message per file, with full Outlook details kept, makes MSG useful for legal review and case work.
Record Keeping
Save proof of approvals, orders and replies as files you can store and find later outside the inbox.
Convert Later
Hold an email as a .msg now, then convert it to PDF or EML when you need to share it outside Outlook.
MSG vs Other Formats
Knowing how MSG compares to other email formats helps you pick the right one:
MSG vs EML
| Feature | MSG | EML |
|---|---|---|
| Format Type | Microsoft binary | Open, plain text |
| Made By | Microsoft (Outlook) | Internet standard (RFC 5322) |
| Opens In | Mainly Outlook or a viewer | Almost any email program |
| Human Readable | No (binary) | Yes |
| Outlook Details | Keeps flags and Outlook fields | Keeps standard email fields |
| Best For | Staying inside Outlook | Sharing across programs |
MSG vs PST
| Feature | MSG | PST |
|---|---|---|
| Holds | One Outlook item | A whole mailbox of items |
| File Count | One file per email | One file for everything |
| Best Use | Saving or sharing single emails | Backing up a full mailbox |
| Both Are | Microsoft Outlook formats | Microsoft Outlook formats |
- You work mainly in Outlook
- You want to keep Outlook details
- You are sharing with Outlook users
- You need single emails as files
- You need a file that opens anywhere
- You want plain, readable files
- You are not tied to Outlook
- You share with mixed email programs
- You are backing up a whole mailbox
- You want one file for everything
- You need contacts and calendar too
- You are moving an Outlook profile
Troubleshooting
Common problems with MSG files and how to fix them:
- No Outlook on this PC: open the file in a MSG viewer instead, or convert it to PDF or EML first.
- Wrong default app: right-click the file, choose Open with and pick Outlook or your MSG viewer.
- Check the extension: make sure the file still ends in .msg and was not renamed.
- Blocked download: a .msg saved from email or chat may be blocked, unblock it in the file properties first.
- This is normal: MSG is a binary file, not plain text, so Notepad cannot show it.
- Use the right tool: open it in Outlook or a MSG viewer to see the real email.
- Need plain text: convert the MSG to EML, which you can read in any editor.
- Open in a full reader: a viewer or Outlook shows attachments you can click and save.
- Embedded message: a MSG can hold another email inside it, open the inner item from the reader.
- Convert to keep them: converting to PDF or EML keeps the attachments with the message.
- What it is: winmail.dat appears when Outlook sends rich text to a program that cannot read it.
- Not the same as MSG: winmail.dat is a TNEF file, though it comes from the same Outlook world.
- Fix at the source: ask the sender to send in HTML or plain text, or use a tool that reads TNEF.
Frequently Asked Questions
Yes. Outlook opens MSG best, but you do not need it. Your options are:
- A free MSG viewer: a tool like the Univik MSG Viewer opens the file and shows the email, with no Outlook needed.
- A converter: change the MSG to PDF or EML, then open it in any reader or email program.
- Some email apps: a few clients and add-ins can read MSG, though support is patchy.
Because a MSG file is not plain text. It is a binary compound file that packs the message, its details and any attachments into one structured file. Notepad only shows the readable scraps and a lot of stray symbols. To see the email properly, open it in Outlook or a MSG viewer. This is the big difference from EML, which is plain text you can read in any editor.
MSG is Microsoft's own format for Outlook, saved as a binary file that keeps every Outlook detail. EML is an open, plain-text format that almost any email program can read. Pick MSG when you stay inside Outlook and want full fidelity. Pick EML when you need a file that opens everywhere.
Yes. A MSG file stores its attachments inside the same file, along with the message text, the sender and recipient details and the date. So when you share a .msg, the whole email travels as one file. This is also why a MSG with large attachments can be several megabytes.
A converter is the simplest way. A dedicated MSG converter can turn one file or a whole folder into PDF, EML, MBOX, PST and more. You can also open the message in Outlook and use Save As or Print to PDF for a single file. A converter is the easier choice when you have many files.
Yes. A .msg file holds a single Outlook item, and that can be an email, a contact card, a calendar appointment or a task. Most MSG files you meet are saved emails, but if you save a contact or an appointment from Outlook to disk, it is also a .msg file.
Apple Mail does not open MSG on its own. On a Mac you can use a MSG viewer or a converter to read the file, or convert it to EML first and open that in Apple Mail. MSG is a Windows and Outlook format at heart, so it travels less easily to other systems than EML does.
Related Tools
Summary: Key Points About MSG Files
- A MSG file is a single Outlook item saved as one file
- Uses the .msg extension
- Binary format, not readable in Notepad
- Made by Microsoft for Outlook
- Keeps Outlook details like flags and fields
- Opens in Outlook or a MSG viewer
- Can hold an email, contact, appointment or task
- Attachments are stored inside the file
- EML is the open, plain-text alternative
- PST holds a whole mailbox, MSG holds one item