A New Zealand accountant was fired for "confrontational" emails with words in red, in bold and in capital letters." Boy, if confrontational emails were a firing offense, I think a lot of people I have worked with would be in deep trouble.
All kidding aside, the woman, Vicki Walker, of Auckland NZ, sued and received money for unlawful termination. I would imagine that if your email style is a problem, your manager should tell you before instantly sacking you.
The truth is that our educational system has not done a great job training people how to write business communication. I have seen emails with all sorts of writing flaws from all lower case, all uppercase, full of misspelling, all the way to those that are to completely nonsensical.