Seth Godin, Get your memo read:
The unanticipated but important memo has a difficult road. It will likely be ignored.
I find this is one of the unexpected challenges of taking on engineering leadership responsibilities. First off, you have to do all the writing things right: use a clear and concise subject, say all the important things up front (probably in bullets!), and develop the important details in thoughtful prose. Even if you nail it there, some people just won’t read, retain, and/or care about the information you have conveyed to them.
Hence: Always Be Repeating Yourself. Always.