Using classic Outlook for Windows in business environments
The Reply option is to reply only to the sender. To send the message to someone who isn't on the To or Cc line, please select Forward. Another alternative is to manually change the recipients when you reply to the message. More information, please refer to: Reply to or forward an email message - Microsoft Support.
Hope this helps!
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.