Multipurpose Internet Mail Exchange (MIME) types instruct a web browser or a mail application how to handle files received from the server. For example, when a web browser requests an item on a server, it also requests the MIME type of the object. Some MIME types, such as graphics, can be displayed inside the browser. Others, such as word processing documents, require an external application to be displayed.
By setting custom MIME types you can determine what applications are used to open a particular type of file on the client side.
To configure MIME types in Plesk, go to Websites & Domains > Apache & Nginx Settings.