Mail does not close and prevents shut down
I turn off the Mail by closing the window thru the "red" buttom and try to close the machine and get an answer that Mail has denied closure. I then two finger tap the icon and select close Mail. Try to shut down again under the "apple" symbol and still get the same denial. I check the icon tray again and the program says it is closed, but the "Mail" toolbar is still open at the top. I go to the "mail" pull down and the "close" is not dark, but I select it anyway. Try to close system again as the "Mail" tray has gone and I can sometimes do a shut down, sometimes not and I just close the lid.
What gives? this has only been happening recently.
MacBook Pro (Retina, 13-inch, Early 2013), OS X Mountain Lion (10.8.4)