I ran into an issue recently where I was trying to retrieve an attachment in an email and it was blocked. Gmail blocks the download of attachments it feels are a risk. Files with certain file extensions (like .exe), zip files that contain them, etc. The full listing and help from Google is here: https://support.google.com/mail/answer/6590?hl=en .

The message you will see is:

Anti-virus warning 
– 1 attachment contains a virus or blocked file. Downloading this attachment is disabled.

I was searching for solutions and a lot of them involve asking the sender to send a different way or use a Google Drive folder or equivalent. In my case that would not work as the file was in an email I sent myself.

Eventually I found this article, which describes how to download the original email, open it in Windows Mail, and download the attachment from there. Very simple, free, and convenient to do. I imagine opening the email in a Mac email client would work as well.