First start out by creating a file named /etc/postfix/rejected_addresses then add the following to it

bad_sender@example.com    REJECT

This will be an hashed map table, so we need to create the hash

postmap /etc/postfix/rejected_addresses

Next we need to add the map to our /etc/postfix/main.cffile. We will be adding this to the smtpd_recipient_restrictions section.

smtpd_recipient_restrictions =
  ...
  check_sender_access hash:/etc/postfix/rejected_addresses,
  ...
  reject_unauth_destination

Once complete reload postfix

postfix reload