[notahacker]

This. More generally, the less attention that goes into perfecting the layout and wording, the more likely the reader is to believe you're on a busy human's to do list and not a mailing list.

HTML layout very bad, neat little bullet points bad, good copy bad, lack of line spacing and excessive terseness good.

[jimmaswell]

So basically be as inefficient as possible

[manicdee]

Be as efficient as possible.

Don't waste time on presentation, so you don't feel like a marketroid.