Function: metamail-region

Process current region through 'metamail'.
Optional argument VIEWMODE specifies the value of the
EMACS_VIEW_MODE environment variable (defaulted to 1).
Optional argument BUFFER specifies a buffer to be filled (nil
means current).
Optional argument NODISPLAY non-nil means buffer is not
redisplayed as output is inserted.

(fn BEG END &optional VIEWMODE BUFFER NODISPLAY)