How to enable Gmail preview?

In Gmail you can view your Emails similar to microsft outlook in pane view. Actually it will splits the previewed mail into pane and mail conversation separately. The pane can be customized as vertical split or horizontal split. You can enable this option at,
 Settings - Labs - Preview Pane - Enable.

And also another great feature called Message Sneak Peak which will preview the email message by right clicking on the mail conversation list.

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