Files that end with extension .olk##Message are not MSG files, rather they are pointers to the original file, and contain very limited information about the email itself. These artifacts are a result of the Microsoft Outlook file structure, and as such often have a very small size of just a few thousand bytes.

Trying to open these files with Outlook would result in the Outlook is not associated with Default Identity error, and they cannot be opened with MSG Viewer for Outlook either.

Either this article or this one may be useful with additional details regarding this issue.