If you are sending an email to a group, and want to discourage people from sending reactionary responses to the whole group, you can use the BCC field in your email application:

• In Outlook, create a new message.
• Click View -> BCC Field
• Enter your own email address in the TO: field
• Enter the group address(es) in the BCC: field

Any replies to the message will only go to you, so if someone wants to send their response to everyone, they will have to enter the addresses manually, if they even know them.