Leo says that Fred is right to be concerned about the security of sending emails because the contents of the messages can be read along the way. If the email is going from one Gmail address to another, however, it would be secure. Ultimately, though, Leo doesn't recommend sending attachments at all. Opening attachments is how most people end up getting infected, and it doesn't just affect that person either. It will spread to all of that person's contacts, affecting their family, business, and the internet as a whole.
Leo recommends putting that attachment up on one of the free upload services like Microsoft's OneDrive, Dropbox, iCloud, or Google Drive. The file can be encrypted to be extra safe. Then instead of sending a file or attachment, he can send a link. Links aren't always safe either, of course, but if his friend is expecting a file from him, then the chances are pretty good it will be safe.