My Apple Mail is very "glitchy" lately. I need to constantly quite and restart Mail or "Rebuild". What happens is, I will get a new email or two into the mail folder, and then some of the new emails suddenly vanish. I restart and they reappear, but this is a hassle. It messes up all my flagged emails. I also have issues unmoving or undeleting emails, as that sometimes happens by mistake. I have a 2011 Macbook Air, which is working fine, other than the need of a new battery. Running El Capitan 10.11.3 Any advice would be appreciated.