Cannot attach a file to outlook email on my iMac.

Update Outlook and macOS first, because Microsoft fixed a recent Outlook for Mac attachment issue in version 16.90.0 and recommends current software when Outlook closes unexpectedly.

1. Install available updates

1. Open Outlook.
2. Select Help > Check for Updates.
3. In Microsoft AutoUpdate, install all available Office updates.
4. On the Mac, open System Settings > General > Software Update and install any supported macOS update.
5. Restart the Mac and test attaching a small file from Finder.

If the Mac is running macOS Sequoia, Microsoft documented an attachment issue as fixed in Outlook 16.90.0. That documented symptom was that nothing happened, rather than Outlook crashing, so updating is still the first action but does not conclusively identify the cause of this crash.^1^

2. Check macOS file access

If Outlook remains open when attaching from one folder but crashes with another:

1. Open System Settings > Privacy & Security > Files and Folders.
2. If Microsoft Outlook is listed, enable access to the relevant Desktop, Documents, or Downloads folder.
3. Quit and reopen Outlook.
4. Test both methods:
   • Attach File > Browse This Mac
   • Drag a small file from Finder directly into the message

As a temporary workaround, use Outlook on the web in an updated browser to send the attachment.^2^

3. Isolate add-ins

If updating and file permissions do not resolve the crash:

1. In Outlook, select Tools > Get Add-ins.
2. Open My add-ins.
3. Temporarily disable or remove recently installed third-party add-ins.
4. Quit and reopen Outlook, then test an attachment.
5. If the crash stops, obtain an updated version from the add-in provider before enabling it again.^3^

4. Determine whether the problem is confined to the Mac profile

1. Open System Settings and search for Users & Groups.
2. Select Add User and create a temporary macOS user.
3. Sign in to that user, open Outlook, and add the affected email account.
4. Test attaching a small local file.

If attachments work there, the failure is associated with settings or data in the original macOS user profile rather than the Outlook installation generally.^3^

5. Reinstall only if the crash persists

Before reinstalling:

• Confirm important mailbox data has synchronized with the mail server.
• Ensure the account credentials are available.
• If this is a managed work or school Mac, consult the organization’s IT administrator first.

Then completely uninstall and reinstall Outlook or Office. Reinstallation is appropriate when application files may be damaged, missing, or incomplete.^3^

If none of these steps works, select Help > Contact Support in Outlook and include:

• Outlook version from Outlook > About Outlook
• macOS version
• Whether drag-and-drop also crashes
• Whether every file and folder is affected
• Whether the temporary macOS user has the same problem

Microsoft maintains the current status of Outlook for Mac problems on its known-issues page.^4^

References

1. Unable to add files as an attachment to emails in Outlook for Mac | Microsoft Support
2. Trouble with Outlook 16.114 on MacOs 15.7.9 - Microsoft Q&A
3. Outlook for Mac not responding, hangs, freezes, or stops working | Microsoft Support
4. Fixes or workarounds for recent issues in Outlook for Mac