I know, I've been in this situation plenty of times. But the thing with emails is that you can word them, and re-word them, as much as you like. When I've been in this position, I open a word document and I just keep working at it until I'm happy. I can think of everything I want to say and hopefully that will do.
Unfortunately, my lecturers are all like "please come to my office and see me about this, I don't like sending long emails" then I scream and die a little inside :l
I forget everything he tells me and the whole thing would have been easier if he just responded through email, but I'm just ranting now..
Anyway, good luck!