So I noticed some lag, horizontal black lines pop up all over my screen, and other oddities. No idea what was causing it at first, but it seems whenever I load Apple's Mail app, the entire OS lags. I started using outlook and it seems to not be an issue any longer. I accidentally opened up the mail app, and it happened again, so I'm pretty certain it's causing it. Anyone else ever have this issue? What the heck could mail be doing? I've used it for years without any issues, and for months now under El Capitan.