Reply to Gmail messages

You can reply only to the person who sent you an email, or to everyone who received the email.  

Reply to messages

1. Open Gmail.
2. Open the message.
3. Below the message, click Reply or Reply to all.

Make "Reply all" your default setting

1. Open Gmail.
2. In the top right, click Settings .
3. Click Settings.
4. In the "Default reply behavior" section, select Reply all.

You can still choose to reply to just one person, but "Reply to all" will be the first option.