When you delete an email message or other item in Outlook, it goes into the Deleted Items folder. You can retrieve it from there at any time over the next 30 days. After 30 days, deleted items are moved into a special hidden folder variously called "Recoverable Items" or "Deleted Item Recovery". Items can be recovered from here using Outlook for Windows or Outlook on the Web, but unfortunately not using Outlook for Mac. After spending 14 days in Recoverable Items, items are permanently and irrecoverably deleted.

There are no backups, restore points, or save states for Microsoft 365 mailboxes.

Microsoft Outlook for Windows

1. Open Outlook.

2. Select your Deleted Items folder.

3. Select the Folder tab in the ribbon and then select Recover Deleted Items.

4. Click an item, select the Restore Selected Items radio button, then click Ok.

   Tip: To select multiple items, press Ctrl as you click each item or click Select All.

Outlook Web App (OWA)

1. Log in to OWA.

2. In the folder list in the left-hand side of the window, click on Deleted Items.

3. At the top of the Deleted Items list click Recover Items Deleted From this folder.

4. Use the resulting window to search for the desired items and select the items you wish to restore by clicking the radio buttons on the left (or click the radio button at the top left to select all).

5. Click Restore from the options in the right-hand pane or right click your selected messages and click Restore from the menu.

Microsoft documentation to recover deleted email messages in Outlook.

For more information on Microsoft Outlook, visit Microsoft's website.