Are you thinking of launching individual topic email newsletters for your subscription site? But you're not sure yet if there's enough interest in any one specific topic?We like the way Help A Reporter handles its new emails devoted to individual topics. There's the "Master HARO" list which has every topic in it but you can opt in to specific topics - the ones in dark print.But HARO also gives you the chance to opt in to the topics in light gray with a blue circle next to them, saying when you c...