Summary
To help protect your computer, Outlook doesn't allow you to receive files of certain types (such as .exe files) as attachments, because of their potential for introducing a virus into your computer.
Body
Overview
To help protect your computer, Outlook doesn't allow you to receive files of certain types (such as .exe files) as attachments, because of their potential for introducing a virus into your computer.
Filetypes blocked by Outlook
View the article Blocked attachments in Outlook to learn which filetypes Outlook blocks by default and how to share your files safely.