To select multiple messages to archive, delete, mark as read, mark as unread, or star, click the check box for each message [1]. You can also press the command key (Mac) or the control key (Windows) while clicking each message you want to select. In the Conversations toolbar [2], click the desired option.
To select all messages, click the command + A keys (Mac) or the control + A keys (Windows).
To select a range of messages, click the first message you want to select, hold down the Shift key, and then click the last message you want to select. All messages between the first and the last messages will be selected.
Note: You can also click the message check box or use the same keyboard command to deselect a message.