set send-verbose

SET SEND-VERBOSE YES/no  -  whether to show where mail is being sent

With the usual YES setting, when you SEND mail, you see a message for
  each address like "abc... Queued.", which confirms that a copy of the
  message is being queued to go to each address.  Once the mail is queued,
  MM runs the sendmail program to start sending it to the address.

If you change it to NO, you will see just the message "Sending... Done"
  with no further information.

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