Difficulties attaching emails (macros?) and difficulties sending emails without replying to a sender

Hi @Sue Devonshire, 

Thank you for posting your question to the Microsoft Q&A forum. 

Based on your description, the problem appears to be related to Microsoft 365 security policies or Outlook configurations. To better understand your situation and the setup, could you please provide us with the following information: 

1. Are you using a business email (e.g., @companyname.com)? Or is it a personal email type (@hotmail, @gmail, @outlook.com)  
2. Are you using the new Outlook or classic Outlook? Or is it a different email client? 
3. Is the Excel file macro-enabled?

In the meantime, as part of the troubleshooting process, I recommend trying the following steps to resolve the issue:

1. Verify attachment handling settings 

Excel files with macros or older formats can be flagged as unsafe. 

• Open the Excel file and check if it contains macros 
• If macros are present, remove them or save the file as .xlsx 
• Compress the file into a .zip before attaching 
• In Outlook, go to File → Options → Trust Center → Trust Center Settings → Attachment Handling  
  • Ensure Turn off Attachment Preview is unchecked 
   
  • Click Attachment and Document Previewers and confirm Excel Previewer is enabled 
  

2. Check macro settings 

Macros can trigger security blocks. 

• Go to File → Options → Trust Center → Trust Center Settings → Macro Settings 
• Select Notifications for all macros (recommended) 

• Avoid Disable all macros without notification 
• Do not choose Enable all macros (high security risk) 

3. Resolve “invalid email” error 

This often occurs due to auto-complete cache issues or recipient validation. 

• Clear the Auto-Complete cache: File → Options → Mail → Empty Auto-Complete List 

• Add the recipient to your Contacts 
  • From the navigation bar, select People. 
  • On the People page, select New contact from the ribbon. 

• Select Save & Close.  For the full guide, please visit: Add, find, edit, or delete a contact in Outlook - Microsoft Support 
• Check Safe Senders list under Home → Junk → Junk Email Options → Safe Senders 
  • Check the boxes on Also trust email from my Contacts and Automatically add people I email to the Safe Senders List in classic Outlook.   

• Select Apply > OK. 
  • Restart Outlook and try sending the email again 

Note: These steps apply to the classic Outlook desktop application. If you are using the new Outlook experience, please let me know so I can provide the correct instructions for that version. 

I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this.  

Thank you for your patience and your understanding. If you have any questions, please feel free to reach out.  

I'm looking forward to your reply. 

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