You can reply to an entire conversation, or to an individual thread within a conversation. When replying to a message, you can choose to reply to the sender only, or to everyone copied into the original message.
First, click on the conversation you wish to reply to.
To reply to the entire conversation, replying only the sender of the last message, click on the Reply button at the bottom of the message. Type your reply text, then click on the Send button
To reply to the entire conversation, including everyone copied into the message, click on Reply to All button at the bottom of the last message. Type your reply text, then click on the Send button
To reply to the sender of a specific thread within the conversation, click on the thread you wish to reply to, then on the Reply button in the top-right corner of the message
To reply to everyone copied into a specific thread within the conversation, click on the thread you wish to reply to, then on the Ellipses in the top-right corner of the message. Choose Reply to All.
The reply pane will show under the message you are replying to. If you prefer, you can show the reply in a new pane, allowing you to return to the mailbox or show another message in the background while you are responding.
Click on the drop-down arrow next to the Reply button in the Reply pane
Choose Pop out reply
The Smart Reply feature scans the email message you have received, and uses machine learning to suggest quick responses. To use a quick response, click on the reply you wish to use - you can edit the response before sending the message.