To reply to an email, you need to select the reply button.
The reply button icon is an arrow that’s turning to the left.
By default if you are in a conversation with many people, which does happen, hitting the reply button replies to the original sender of the email.
Though if you use the nearby dropdown menu by clicking on the three vertical dots, you get the option to reply to all.
Username or Email Address
Registration confirmation will be emailed to you.