MAIL flashing between home page and 1 email trying to send
MacBook Air (13-inch, Mid 2013), OS El Capitan. Tried to send email with 2 page WORD attachment. Now that email window is flashing repetitively, but the email is not sending. I've shut down MAIL, and have restarted the computer. Same issue starts all over again when MAIL is opened. Very odd... Paralyzing MAIL but other apps unaffected. Can't get it to stop and can't catch the flashing email window to delete it.
Additionally I can see that on the main MAIL page, I have received a dump of about 80 emails which normally go to my junk email account on MyYahoo.
MacBook Air (13-inch Mid 2013), OS X El Capitan (10.11)