Quick Comparison
| Feature | MSG | EML |
|---|---|---|
| Full name | Outlook Message | Electronic Mail (MIME) |
| Extension | .msg | .eml |
| Format type | Binary OLE/CFB + MAPI | Plain-text MIME (RFC 5322) |
| Created by | Microsoft Outlook | Gmail, Apple Mail, Thunderbird, most clients |
| Encrypted by default? | No | No (unless S/MIME) |
| Open without Outlook? | Needs a viewer | Yes — almost any client |
| Readable in a text editor? | No (binary) | Yes (headers + body) |
| Best free opener | JustToolkit MSG Viewer | JustToolkit EML Viewer |
When you see MSG vs EML
MSG usually means someone saved or dragged a message out of Microsoft Outlook. Legal teams, support desks, and backup tools also export batches of .msg files. The body, recipients, and attachments live in MAPI properties inside an OLE compound file — the same family of containers used by older Office formats.
EML is the internet-native format. When you “download message” from Gmail, export from Apple Mail, or archive mail in Thunderbird, you typically get .eml. Because it is MIME text, you can open it almost anywhere and even inspect raw headers for spam analysis.
If the file is named message.rpmsg, you do not have MSG or EML — that is rights-protected mail. See RPMSG vs MSG vs EML or use the RPMSG Viewer.
How to open each format free
Open MSG without Outlook
- Go to the free MSG Viewer.
- Drop the
.msgfile — parsing stays in your browser. - Read subject, parties, body, and download attachments.
Open EML anywhere
- Double-click in Apple Mail / Thunderbird, or import into Gmail.
- Or use the free EML Viewer for a quick browser preview.
- For forensics, open the file in a text editor to inspect raw headers.
Recommendation
Use EML when you need maximum compatibility and long-term archives. Use MSG when you must preserve Outlook-native properties from an existing export. Do not convert blindly before checking whether the file is actually RPMSG (encrypted).
Related: MSG vs EML · RPMSG vs OME · All tools