File showed up Sunday, March 12, 2017. File contains - "Important Warning!!! Don't create or copy files inside this folder manually, they are managed by the Akonadi framework!" I did add Google Calendars that day and maybe 2 email accounts if that helps.
This file is created by the iCal/vCard folder resource. I guess you somehow accidentally set up your home folder as a source folder for one of those. Make sure none of your calendars or addressbooks point to your home folder, then you can safely remove the file.
This just happened to me after I tried to add a Google Calendar iCal thingy to KOrganizer.