See the full article at https://support.office.com/en-ZA/Article/Restore-deleted-items-in-Outlook-cd9dfe12-8e8c-4a21-bbbf-4bd103a3f1fe

Accidents happen. When that sudden realization hits days later that you need an email message that’s long gone, the Recover Deleted Items command might save your day. You can recover some deleted items, like messages, appointments, contacts, tasks, and notes, even after the Deleted Items folder is emptied or you’ve “hard deleted” an item by pressing Shift+Delete. This feature requires a Microsoft Exchange Server account and doesn’t work with POP3 or Internet Message Access Protocol (IMAP) accounts.

If you’re using Office 365 or another Exchange-based client, you can also restore deleted items using Outlook Web App. For more information, see Recover deleted messages or items in Outlook Web App.

1. Click Folder > Recover Deleted Items.

   

   If you don’t see Recover Deleted Items, you’re probably not using an Exchange account or you don’t have a folder selected in that account.

2. Click the message you want to recover, and then click Recover Selected Items .

   TIP    To select multiple items, press Ctrl as you click each item, and then click Recover Selected Items .

   Recovered items are restored to the folder you’re working in.