Value,Description,Reference
fax-message,"Indicates a message whose primary content is a fax     
mail message.  The primary content is image data.
The context is usually a message recorded from
a facsimile telephone call.",[RFC3458]
multimedia-message,"Indicates a message whose primary content is           
a multimedia message.  The primary content is
multimedia, most likely MHTML.  The context is
often spam or newsletters.",[RFC3458]
None,Indicates an unknown message context.,[RFC3458]
pager-message,"Indicates a message whose primary content is a page.   
The primary content is text data.  The context is
an urgent message usually of a limited length.",[RFC3458]
text-message,"Indicates a classic, text-based, Internet message.",[RFC3458]
video-message,"Indicates a message whose primary content is a video   
mail message.  The primary content is video data.
The context is usually a message recorded using
a video camera, or a message whose primary purpose
is to contain an external reference to a message
recorded using a video camera.",[RFC3938]
voice-message,"Indicates a message whose primary content is a voice   
mail message.  The primary content is audio data.
The context is usually a message recorded from
a voice telephone call.",[RFC3458]