While cleaning up email to get rid of the large amount of junk I sort by correspondent. This allows me to select several of the mostly junk emails together to delete them. I highlight the first email I want to delete, go to the last one and hit shift and click. Sometimes that can be over a hundred or so emails to delete at once. After selecting delete, sometimes they don't all delete. The email is no longer bolded as though I had read it, but only a portion of the selected actually delete. It sometimes takes 2, 3 or more times of selecting them to get them to all delete. This has just been recently, within the past few months that I have noticed this. Not a terrible problem, but curious as to why this happens.