The Junk Email Filter is to keep junk email messages, also known as spam, from cluttering your Inbox. By default, the Junk Email Filter turned on, and the protection level sets to Low, the setting designed to catch the most obvious spam. Messages detected by the Junk Email Filter moves to the Junk E-mail folder. The instructions can be found in the Files section which is located at the bottom right or click here: Managing Junk Email in Office 365