To make sure your e-mail gets read, write less.
People have a tendency to read something when it’s short. It doesn’t give them an excuse to read this later.
To ensure that your short e-mail contains all the points that you need to put across, consider using the inverted pyramid, making sure that your most important points are said before anything else is.
Keep things as short as they possibly can, without losing any information. Learn about Occam’s razor, and apply it to all your writing.
Proof? I’m guessing that you read this post was read in its entirety, didn’t you?