I say all of this, because I used to think email promos were a waste. Until I saw the design my agent inherited from her super talented designer Ophelia Chong. Every week, or every other week my agent Alyssa will send out an email promo of the latest new images of her photographers, that work. Weeks or months may go by that my images don't make the cut. That only means I don't have the images that are worth the money or the time, to send the darn things out.
I think all marketing is helpful, but good marketing, is being smart about your choices. Your images, your design, and layout need to stand out, showcase your strongest work, or you will.. get lost in the crowd.