If you are not using it with Exchange server then you can't recover deleted emails.
However even if you are using Exchange server still there is some time period set by the administrator, in which you can get back your deleted emails.
This depends upon the retention time specified by Your Exchange administrator. Items that are deleted permanently on the server running Exchange will be there for specified time. After this time elapses, you cannot recover the deleted items.
You can recover the deleted emails by following below mentioned steps.
In the folder from which you have deleted the emails or Deleted items folder , Click Tools menu → Recover Deleted Items.
In case you are not able to see the Recover Deleted Items option then you should use an exchange account to make it visible.
Select the item / items to recover and click Recover Selected item. This will allow each item to get restore at its previous location from where it was removed.