Same here - I have no big problem with emails but phone calls and conversations can be a lot more difficult.
If you can express yourself OK with WP posts, why not try typing your email into a WP posting box, as if it were a WP message, and then copy and paste it into an email instead of hitting the "post" button? Might just work. There's got to be some reason why you get hung up with an email to a particular person but not with a post to a particular group. Maybe it's something to do with how you see the recipients? I'm always quite mindful of who I'm writing to, and it does make writing harder if I feel that the reader is going to be difficult in any way. So if I was emailing my boss then I'd find it hard to speak my mind freely, if I was emailing a partner I might worry a lot about saying all the expected little courtesies and reassurances, but with posting on a board like this I feel pretty free to just make a point or tell a story without doing any harm.