If you often exchange group emails, setting Reply all as your default reply setting can help ensure no one is ever left out of the conversation. To enable this feature, sign in to your Gmail account, click on the gear button, and then select Settings:
Ensure you have selected the General tab at the top of the window; then, scroll to the section Default reply behavior. To activate the feature, select Reply All. If you would like to continue using single reply, select Reply:
In order for the change to take effect, ensure you click Save changes at the bottom of the General Settings page.