All you need to do is follow the steps below:
In the left side navigation panel, click the name of the email folder that you want to read.
To open a specific message, click the corresponding mail row.
Double click the subject to open the message in a new tab.
The inbox tab remains open. You may open several messages as separate tabs.
Alternatively, press the Enter key to open the message in a new tab.
When you finish reading the message, close the tab to return to the message list of the current folder.