Force Splotlight to search a subfolder
Spotlight considers anything in Library (all of them: /System/Library, /Library, and ~/Library) to be a "System file". (Exception: Yosemite considers /System/Library/CoreServices to be an applications folder and not a system files folder.) By default, it won't find such files unless you start inside the Library folder or add "System files" "are included" to the search terms. (If you don't see "System files" as an option, select "Other". Scroll through the list to find "System files", or instead of scrolling start typing "System files" in the search field. Optionally, turn on the check mark to add "System files" to the menu so you won't have to look for it again.)

Anything whose name starts with a period (like .olk14Message in your case) is considered invisible. Spotlight won't find anything that's invisible or in an invisible folder unless you either start in the invisible folder or add a search term for "File visibility" that says to report invisible items.

mdimport won't help here. Spotlight has already indexed even System files and Invisible files. It just won't show them to you unless you specifically ask for them.

For mdutil -E ..., you need to specify a volume, not a folder. Thus, for example, mdutil -E / would erase (and probably rebuild) the Spotlight index for your entire boot volume. You can't select anything smaller than a volume.