If you are not a fan of how gmail groups your emails together, you can actually turn that off. I had a teacher contact me this morning concerned because he missed emails because of it. If you want to turn it off, I posted a tutorial on my "Guides & Tutorials" page today. Go check it out!
I had a teacher ask me if there was a way to hide or remove students who are no longer in your class. The answer is maybe. It depends on if they are officially dropped from your class and appearing as red in your roster and gradebook. If not, then no, you cannot remove them until they have been unenrolled from the class. If the student is showing up as red in your gradebook though, you can hide them so you don't have to worry about them. Here is a screenshot to help you do it: