Mail suddenly fails to open, it starts then goes to beachball
email fails to open (application not responding).
I click on the mail icon, it seems to start for moment, then immediately stops responding.
I can find some of my mail in the icloud but only a small portion.
imac 21.5, late 2013 build, el kapitan, 10.11.6
iMac 21.5″, OS X 10.11