First, when you delete something it should be in the Trash folder for two weeks. After that it drops into the "Deleted items" folder which is hidden, and stays there for about another 30 days. To look at it, right-click on the Trash folder and you will see a menu with that option. Click on that and you will be able to recover anything still in that folder. Other than that your only recourse would be to not send emails to Trash, but to another local folder you create or already have. Only Spam and Trash are subject to a deletion schedule. Emails will remain until you delete them in all other folders.
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