Hey there, let's work through this frustrating Excel attachment issue in Outlook 365. I’ve helped troubleshoot similar problems plenty of times, so here are targeted fixes to get things working again:

• Double-check the Excel Previewer is enabled in Outlook
  It’s easy for the previewer to get accidentally toggled off. Here’s how to confirm:

  1. Open Outlook, go to File > Options > Trust Center
  2. Click Trust Center Settings > Attachment Handling
  3. Make sure "Turn off Attachment Preview" is not checked
  4. Click Attachment and Document Previewers – ensure "Microsoft Excel Previewer" has a checkmark. If not, enable it and restart Outlook.

• Repair your Office 365 installation
  Corrupted Office files are a top suspect here. Try this:

  1. Open Control Panel, go to Programs > Programs and Features
  2. Find "Microsoft 365" in the list, right-click it and select Change
  3. Start with Quick Repair (it’s quick and doesn’t need internet). If that doesn’t fix it, go for Online Repair – this will reinstall any missing or damaged components, so make sure you have a stable connection. Restart your PC after the repair finishes.

• Fix Excel file associations
  If double-clicking the attachment does nothing, the file type might be linked to the wrong app:

  1. Open Windows Settings, go to Apps > Default Apps > Choose default apps by file type
  2. Look for Excel file extensions like .xlsx, .xls, .xlsm
  3. Make sure each is set to "Microsoft Excel" (not a viewer app or third-party tool). If not, click the current app and select Excel from the options.

• Adjust Outlook’s Trust Center settings
  Strict security settings can block attachments from previewing or opening. Test this temporarily:

  1. In Outlook, go to File > Options > Trust Center > Trust Center Settings > Attachment Handling
  2. Uncheck "Enable Protected View for attachments received from the internet" (if this fixes the issue, add the sender to your Safe Senders list instead of keeping this off long-term)
  3. Also try unchecking "Enable Protected View for attachments that are potentially unsafe" to see if that helps.

• Re-register the Excel Previewer via Command Prompt
  Even if you checked the registry before, re-registering the previewer components can resolve hidden issues. Do this:

  1. Open Command Prompt as Administrator
  2. Run these commands one by one (adjust the path if you have 32-bit Office on 64-bit Windows – use C:\Program Files (x86)\... instead):

     regsvr32.exe "C:\Program Files\Microsoft Office\Root\Office16\EXCEL.EXE" /regserver
     regsvr32.exe "C:\Program Files\Microsoft Office\Root\Office16\EXCELVIEW.DLL"
     

  3. Restart your PC and test the attachment preview again.

• Troubleshoot conflicting add-ins
  Third-party add-ins in Outlook or Excel can interfere with preview/opening. Test in safe mode:

  • For Outlook: Press Win + R, type outlook /safe and hit Enter. If preview works here, go to File > Options > Add-ins > Go... (next to COM Add-ins), disable all add-ins, then re-enable them one by one to find the problematic one.
  • For Excel: Open Excel in safe mode with excel /safe (via Win + R). If opening the attachment works here, check Excel’s add-ins the same way to identify conflicts.

内容的提问来源于stack exchange，提问作者Graca Mateus Assane