SepticSceptic:There's a strategy to this that I've found helps immensely. Start it with something of a table of contents or a readers digest version which will stick in peoples minds should they only read that bit and trash it. Should they not read the rest and then wonder why something's not right as a result of something they've failed to comprehend they'll at least recall something from that and hopefully dig it up from file13. For the content itself follow the format of the beginning, expanding it and placing the repeated and important parts in bold.
I usually find that most people won't read more than the first couple of sentences, especially in a technical email.
I have started to use numbered lists, and brief and consise sentences .
Though sometimes it's easier to make a quick ph call,
The parts that are highlighted in bold, when skim-read, will help make the reader realise the importance of what they're reading and hopefully they'll read the whole thing if required. Keep the reader's interest by adding images or diagrams. Depending on the audience try to include a touch of humour