File Extension MSN File Format Network document (Microsoft) MSN stands for Network document (Microsoft). This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Need to open network diagram One computer cause another on the network to slow down Do I need my small business server?