I turned off the Mail's RSS feed services--deleted all feeds, switched back to Safari RSS as default, and turned of updating, and have had no further problems with the sqlite files showing up in trash so far, and it usually happens about once a day in the mornings for me...
So, either mail RSS is messed up, or the conflict between having both Mail and Safari update RSSs was generating the file.
I suggest going back to Safari RSS and killing all Mail RSS functions.