“If your message requires several paragraphs add a subhead before each paragraph so the email is easier to skim. People are always looking at your email, wondering to themselves “How is this relevant to me?” It’s easier for them to read 3 bold sentences rather than 3 paragraphs. If those subheads speak to them then they’ll read the paragraphs for more detail.”
Jamie Dihiansan of Basecamp, speaking about email on Campaign Monitor’s blog