Outlook and temp files are lost. Why? How can I protect myself from this problem?
To avoid this problem in the future, instead of opening attachments directly from the email, right-click on the attachment and choose to "Save As" the file so you can select where you want the file saved (e.g., your Documents or Pictures folder).
Then open the file from Windows Explorer instead. But if you really want to know, Windows does store the message. The actual storage location will vary. And it is strange.
User > AppData > Local > Microsoft > Windows > Temporary Internet Files > Content.Outlook > 9PDH6FAT.
To determine that location, go through the steps to do the Save As, and note the default location. But the next time it may change. So remember to do the Save As and specify the location.