File Extension SM File Format Maillist (SoftSpoken Mailer) SM stands for Maillist (SoftSpoken Mailer). 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 SAP: What's the difference between AL08, SM04 and SM51? smart forms and sap script Is there a difference between SM30 and SM31?