Long emails, long sentences, long excuses and long explanations. Eventually your audience will get bored of them. I have in the past been extremely guilty of that. Partly, I'd say, because of the traditional writing culture in Portugal. There is an abundance of asides and inclusions in speech with parentheses and commas.
But it's a bad habit.
How short is short enough? Apparently, anything larger than 7 chunks of information at a time is too much. And so, each sentence, paragraph, list and rationale should be kept at a maximum of 7 chunks of information. Probably its better to keep it at lower quantities still.