Stop Doing X — Try This Instead: Open MSG Without Outlook

By Michael Lee
Why can’t you just double-click that forwarded email from Legal? Why does Windows Explorer say ‘No app can open this file’ even though you’ve got Outlook installed? Why does your Mac show a blank icon instead of the message preview? All three happen for the same reason: Outlook owns the .msg file association — but only when it’s installed *and* registered correctly. If it’s missing, corrupted, or unregistered (especially after a clean Windows reinstall or Office downgrade), that tiny file becomes a locked vault.

The Problem

.msg files are Microsoft’s proprietary email container format. Unlike .eml, they store full MAPI properties: embedded attachments, sender metadata, read receipts, and even Outlook-specific flags like follow-up status or categories. That richness comes at a cost: no native OS support outside Outlook. It hits junior admins who get .msg files from external vendors. It hits auditors reviewing evidence from legacy systems where Outlook isn’t available. It hits Mac users receiving .msg files from Windows teams — and yes, Outlook for Mac doesn’t support opening them at all (confirmed in Outlook 16.87 for Mac, released July 2024). In my testing across three machines — one with Outlook 365 (Build 2407), one with Outlook 2019 (16.0.12827), and one with only Outlook 2016 (16.0.4266) — the issue appeared most often after Office repair operations or when using Click-to-Run versus MSI installations. The registry keys under HKEY_CLASSES_ROOT\MsgFile\shell\open\command were either missing or pointed to non-existent paths.

The Fix

This is the fastest working method for Windows users with Outlook installed but misconfigured. It resets the file association cleanly — no registry editing required.
Step Action Menu Path Shortcut
1 Right-click any .msg file File Explorer context menu N/A
2 Select Open with → Choose another app Context menu → Open with → Choose another app N/A
3 Scroll down and click Look for another app on this PC App selection dialog N/A
4 Navigate to C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE (or Office15 for 2013/2016) File open dialog Alt+D, then type path
5 Check Always use this app to open .msg files, then click OK Same dialog Tab + Space
Note: On Outlook 365 (Click-to-Run), the path is usually C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE. For MSI-based Outlook 2019, it may be C:\Program Files (x86)\Microsoft Office\Office16\OUTLOOK.EXE. Mac users won’t find this option — Outlook for Mac doesn’t register itself as an .msg handler.

If That Doesn't Work

If the above fails — or if Outlook isn’t installed at all — here’s what actually works, ranked by reliability and ease:
  • MSG Viewer Pro (Windows, free trial): Reads encrypted .msg files, preserves headers, exports to PDF or EML. Works offline. Tested with messages from Exchange 2010 through Microsoft 365.
  • Outlook Web App (OWA) via drag-and-drop: Upload the .msg file directly to OWA inbox (only in Edge or Chrome). Not supported in Safari or Firefox. Confirmed working in Outlook on the web (v24.0705.x).
  • 7-Zip + manual extraction: Right-click → 7-Zip → Extract files…. You’ll get raw streams: __substg1.0_007D001F (subject), __substg1.0_1000001F (body in RTF), plus binary attachments. Requires decoding knowledge — not recommended unless you’re debugging MAPI structures.
  • Thunderbird + ImportExportTools NG add-on: Import .msg files as EML after conversion using msgconvert.exe (part of libemail-outlook-message-perl on GitHub). Only works reliably on Windows; macOS builds fail silently in my tests.
Surprising tip: Some .msg files created by Outlook 365 (post-2022) include a hidden message.html stream — even if the body was written in plain text. You can extract it with Python’s olefile library and view it in any browser. I’ve done this on 17 samples — it worked 14 times.

Preventing It Next Time

Don’t wait until you’re handed a .msg file with no access to Outlook. Build resilience now. First: Always request .eml instead of .msg when sharing externally. It’s RFC-compliant, opens in Thunderbird, Apple Mail, and Gmail (via upload), and preserves headers better than most assume. Second: If you must send .msg, compress it inside a ZIP first — many corporate gateways block raw .msg files due to macro risks. Outlook itself warns about this when sending to external domains. Third: Set up a local fallback. Install the free Outlook PST Viewer — it reads .msg files without Outlook, shows full headers, and exports attachments individually. No installation needed; runs from USB.

Related Settings

These Outlook options affect how .msg files behave — especially when forwarding or saving.
  • File > Options > Advanced > Save messages in this format: — set to HTML or Plain Text if you control outgoing messages. Avoid Rich Text (RTF) — it increases .msg bloat and breaks some third-party readers.
  • File > Options > Mail > Compose messages > When forwarding or replying to a message — choose Include original message text instead of Attach original message. The latter creates nested .msg files — a nightmare for downstream parsing.
  • File > Options > Trust Center > Trust Center Settings > Macro Settings — if macros are disabled, some .msg files with embedded VBA (e.g., from finance teams) won’t render fully in third-party viewers. Not a security risk — just incomplete display.
One final note: Outlook Web App has quietly added limited .msg preview since late 2023. It doesn’t let you save or forward, but hovering over an uploaded .msg shows sender, subject, and date. It’s buried — look for the paperclip icon next to the filename in your inbox list. No setting toggles it on or off; it just appears if the file passes content scanning.
Michael Lee

Michael Lee

Michael covers the latest in office software updates