Yeah, I have the same problem, I've let a number of opportunities slip through my fingers that way.
Maybe you should get drunk and then email?
Or pretend you're someone else? Or get someone else you can trust to type the message and send it?
I think it's something you just have to get over, like when you're little and you don't dare jump down anything more than three feet. Once you start doing it though, it becomes easy and fun.