The <prohibitedfiles> element defines file types that course participants (students, teachers, teaching assistants, etc.) are prohibited from uploading into assignment dropboxes, grading screens, announcements, and discussion forums.

This setting does not restrict course author uploads.
<prohibitedfiles extensions="string"/>
prohibitedfilesextensionsA comma-separated list of prohibited file extensions. Do not include the period for the extensions. For example, this is a valid value: mov,mp4,mp2,avi,m2v,d2v,d3v,dv,dvx,f4v
See Also
Domain Customization