set control-d-automatic-send

SET CONTROL-D-AUTOMATIC-SEND NO/yes  -  whether to send automatically

With the usual NO setting, outgoing messages are not sent when you use 
  control-d to finish typing them; instead, you see the Send> prompt and
  can choose whether to send or quit.  

If you change it to YES, then if you use control-d to indicate the end of
  your message, it will be sent immediately.  This saves you one command,
  but also makes it possible for you to send accidentally.

For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show   set escape-automatic-send
(at the MM> or Read> prompts:)  send
(at the Send> prompt:)  send