Get Out of the Way of the Message
Getting an email opened is only the first step. If you write the sequel to War and Peace, pack the message with visual clutter, or otherwise turn reading your email into work, guess who will go on to something else?
Chunk it Up
If the email is longer than a paragraph or two, use techniques like subheads, bullets, or numbered lists, to make it easy for people to read.
From 10 WAYS TO MAKE PEOPLE ACTUALLY READ YOUR EMAILS (By Erik Sherman, business and tech writer for Inc, The New York Times Magazine, Fortune, and more.)