message-send-method-alist

message-send-method-alist is a variable defined in `message.el'.
Its value is

((news message-news-p message-send-via-news)
 (mail message-mail-p message-send-via-mail))

Documentation:
Alist of ways to send outgoing messages.
Each element has the form

(TYPE PREDICATE FUNCTION)

where TYPE is a symbol that names the method; PREDICATE is a function
called without any parameters to determine whether the message is
a message of type TYPE; and FUNCTION is a function to be called if
PREDICATE returns non-nil. FUNCTION is called with one parameter --
the prefix.