An unexpected or suspicious email should never be opened without consideration because it could contain a virus that can harm your computer, steal saved information, and render your computer useless.
As a general rule, only open attachments if you are expecting them or know the person and if they are relevant to what you are doing. .exe files can run a program, and there is no reason to share them. If you get one, you should delete it.
Google has a filter in place that prevents the sending of .exe files, which can also be distinguished in zip folders. If you receive an email with a zip, open the folder to discover a .exe extension. Some attachments might slow the computer down. Most legit emails have some salutation. Most elicit emails provoke a sense of urgency in the user and cannot be trusted.