So what should I use in business practice?
Encrypted email messages
The simplest manner to securely exchange files via email is to send an encrypted attachment by using 7-Zip or WinRar. Send the password via another channel such as an SMS. Unfortunately, email only works for files of 10 to 15 MB max.
Private cloud or on-premise file sharing tools
If you only need to share big files with someone occasionally, there are safe web-based solutions such as Hightail that enable you to simply upload a file and enter the recipient’s email address. Your recipient will then receive an email with a link that contains a randomly generated string (a password, in effect). Some public available tools, like DropBox, OneDrive or WeTransfer offer the same service but are, however, less secure. If requested by a law enforcement agency these firms might be forced to disclose your files.
If you exchange files with certain people regularly it may be better to set up a shared space, such as Microsoft SharePoint, to which access is granted by means of a username and password.
To err on the side of caution, you can set up the secure file sharing tools in an on-premise configuration or in a private cloud supplied by a provider falling under a jurisdiction of your choice. This way, you are optimally protected against breaches of confidentiality, integrity and non-repudiation.