mailcap

text/html;                w3m -I %{charset} -cols 2000 -T text/html -dump; copiousoutput
text/plain;               less
text/rtf;                 $HOME/.mutt/view_attachment.sh %s rtf
text/directory;           $HOME/.mutt/view_attachment.sh %s

image/gif;                $HOME/.mutt/view_attachment.sh %s gif
image/jpeg;               $HOME/.mutt/view_attachment.sh %s jpg
image/jpg;                $HOME/.mutt/view_attachment.sh %s jpg
image/pdf;                $HOME/.mutt/view_attachment.sh %s pdf
image/png;                $HOME/.mutt/view_attachment.sh %s png

application/msword;       $HOME/.mutt/view_attachment.sh %s "-"
application/octet-stream; $HOME/.mutt/view_attachment.sh %s "-"
application/pdf;          $HOME/.mutt/view_attachment.sh %s pdf