Fixing Outlook on the Web Issue on Mac: Emails Showing as “Partially Downloaded”

by

Outlook on the Web (OWA) is widely used across macOS devices for quick access to Office 365 mail without installing the full Outlook desktop app. But recently, some Mac users—especially those using Safari—have reported a frustrating issue:

Emails show as “partially downloaded,” and users cannot open or view the full message.
This issue also appears on Chrome/Firefox on Mac in some cases, making it seem like the mailbox is corrupted. However, the root cause often lies somewhere else.

Symptoms

Users may experience one or more of the following:

  • Emails display only a portion of the content
  • Messages load endlessly or appear blank
  • Attachments fail to appear
  • Outlook Web starts behaving inconsistently only on the Mac device
  • Works normally on Windows or mobile apps

Root Cause: Browser Cache + Network Instability

Based on the troubleshooting carried out, the issue primarily occurs when:

  • Internet connectivity fluctuates (low bandwidth, unstable Wi-Fi, VPN interruptions, proxy issues), and
  • Browser cache becomes corrupted or stale, especially in Safari.

Safari maintains aggressive caching and local storage for modern web apps like Outlook, and when connectivity is weak, Outlook fails to properly fetch message bodies.
This results in OWA displaying the message as partially downloaded, even though the actual mailbox data in Microsoft 365 is healthy.

Good news — the problem is local to the browser, not the mailbox.

How I Fixed the Issue

To restore Outlook on the Web on macOS, here are the steps that resolved the problem instantly:

1. Reset Safari using a Safari Reset Script

Safari does not have a built-in “Reset Safari” option like older macOS versions.
So I used a Safari Reset Script that:

  • Clears cache files
  • Deletes corrupted local storage
  • Removes temporary data
  • Resets session caches and web data

Reset Safari to default settings

  1. Open a Terminal window: Applications > Utilities > Terminal
  2. Backup your bookmarks (optional). Copy-paste the following code into Terminal:
    cp ~/Library/Safari/Bookmarks.plist ~/Desktop/Bookmarks.plist;
  3. Force Safari to quit:
    killall Safari;
  4. Clear cache, cookies and Safari folders (copy-paste each line separately):
    rm -Rf ~/Library/Cookies/*; rm -Rf ~/Library/Cache/*; rm -Rf ~/Library/Safari/*;
  5. Remove some stubborn files and settings (copy-paste each line separately):
    rm -Rf ~/Library/Caches/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery; rm -Rf ~/Library/Caches/Metadata/Safari; rm -Rf ~/Library/Caches/com.apple.Safari; rm -Rf ~/Library/Caches/com.apple.WebKit.PluginProcess; rm -Rf ~/Library/Cookies/Cookies.binarycookies; rm -Rf ~/Library/Preferences/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery; rm -Rf ~/Library/Preferences/com.apple.Safari.LSSharedFileList.plist; rm -Rf ~/Library/Preferences/com.apple.Safari.RSS.plist; rm -Rf ~/Library/Preferences/com.apple.Safari.plist; rm -Rf ~/Library/Preferences/com.apple.WebFoundation.plist; rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginHost.plist; rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginProcess.plist; rm -Rf ~/Library/PubSub/Database; rm -Rf ~/Library/Saved\ Application\ State/com.apple.Safari.savedState;
  6. Restore your bookmarks (optional). Copy-paste each line separately:
    rm -Rf ~/Library/Safari/Bookmarks.plist; cp ~/Desktop/Bookmarks.plist ~/Library/Safari/Bookmarks.plist;

Once Safari was cleaned and relaunched:

✅ Outlook Web started loading full emails
✅ “Partially downloaded” message issue disappeared
✅ Emails opened instantly across OWA tabs
✅ No impact on user bookmarks or saved passwords

If using Chrome or Firefox on macOS, clearing browsing data (cache + cookies + site data) achieves the same fix.

Why This Fix Works

Outlook Web relies heavily on IndexedDB, local storage, WebKit cache, and browser-level session tokens.

When connectivity drops mid-session:

  • Messages partially sync
  • Browser records incomplete data
  • Outlook Web cannot re-validate the cached message
  • The browser keeps showing the incomplete version instead of redownloading

Resetting Safari forces OWA to fully reload the mailbox from Microsoft’s servers.

Conclusion

If Outlook on the Web on your Mac is showing emails as “partially downloaded” and refuses to open messages, the issue is not with Microsoft 365 or Exchange Online.
It is usually caused by corrupted browser cache due to unstable internet connectivity.

A simple Safari reset resolves the issue instantly.

This fix helps avoid unnecessary mailbox repairs, profile recreations, or user downtime.

If you want the Safari reset script shared, or would like a downloadable version, I can prepare that as well.

!!! THANKS FOR READING !!!

Regards,
HARISH KUMAR

Knowledge is not a finite resource to hoard; it’s a boundless treasure that grows when shared

Leave a Comment