I recently taught a course that covered communication skills and email style, reminding me of the following (via Peter Klein):
Years ago, I was participating in an email discussion with Heckman, who made all of his contributions to the conversation IN ALL CAPS.
As I recall, I privately emailed him to suggest — diplomatically, I hoped — that if he didn’t find the shift key convenient, he could just eschew upper case altogether and type using only lower case, like e.e. cummings. You see, I explained, using all caps gives other readers the impression that you are shouting.
“I AM SHOUTING!” he emailed back.