That is true. I wanted to email my tax data to my accountant. So, I made a self-extracting PGP archive several megabytes in size. Gmail wouldn't let me send it

That is true. I wanted to email my tax data to my accountant. So, I made a self-extracting PGP archive several megabytes in size. Gmail wouldn't let me send it until I tacked on .remove after the .exe extension. It's not really an unreasonable thing, IMO. Google is just making sure the file won't run semi-automatically upon being downloaded. Ending in a random extension prevents that, since the user has to deliberately rename the file first.