Gmail has a hidden preview panel that gives you a dual-pane view of your emails—just like in Outlook and other desktop email clients. Here’s how to enable it on the web and choose a horizontal or vertical split.
First, head to your Gmail inbox. Click the Settings cog and then click “Settings.”
Choose the “Advanced” tab.
The Preview Pane option is towards the bottom. Choose “Enable” and then click “Save Changes.”
You’ll be taken back to the Inbox, where a new “Toggle split pane mode” button will be visible next to the Settings cog.