There is no built-in functionality in Outlook to prevent that. The usual workaround is to add the address to the BCC line and leave the To/CC fields empty, so that pressing the reply/reply all button results in empty address line.
Disable reply all on some composed emails
Aran Billen
806
Reputation points
Hi all,
Is it possible to stop users using "reply to all" button when I send select emails to others?