set default-send-command

SET DEFAULT-SEND-COMMAND [command]  -  define an automatic Send> command

The DEFAULT-SEND-COMMAND defines a command to be executed automatically 
  when you press RETURN at the Send> prompt.  It can be set to nothing,
  so that no command is executed.  The usual setting is nothing.

The most common alternative is the SEND command (Send Mode), so that
  when you get to the Send> prompt, pressing RETURN sends the message.
  This makes it easier for you to send accidentally.
  
To unset, type SET DEFAULT-SEND-COMMAND with nothing following.

For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show
(at the Send> prompt:)  ?