Not allowing replies to sender

Outlook and Exchange do not provide a way to technically block or suppress replies from Bcc recipients to the sender. Any recipient (To, Cc, or Bcc) who receives a message can always choose to reply.

Only best‑practice guidance is available:

• Use Bcc primarily to keep recipient lists private, to reduce Reply All storms, or to remove people from a conversation when they no longer need the extra email.
• Do not use Bcc for sensitive scenarios (for example, secretly including a manager). Instead, send or forward a separate message to that person.
• If replies from Bcc recipients would be problematic, avoid putting them on Bcc and instead send them a separate, explicit message where expectations are clear.

There is no supported configuration in Outlook or Outlook on the web that enforces “no reply” behavior specifically for Bcc recipients.

References:

• Outlook Best Practices: Write great email
• Show, hide, and view the Bcc (blind carbon copy) field in Outlook for Windows