According to Ken Magill, Yahoo might start blocking images in HTML email by default, requiring your recipients to click a "show images" button if they want to see all your pretty graphics.
But if you’re Goodmail certified, they’ll keep your images on by default.
It’s unconfirmed, but I’m inclined to believe it. I think Yahoo is basically testing the waters and seeing what kind of push back they get from all this. You may recall that AOL got quite a lot of complaints about this when they first announced their partnership w/Goodmail. I doubt anybody will complain this time around.
For those of you who don’t know, blocking images is a common safety measure that more and more email programs are implementing in order to protect their users’ privacy. If your email designers aren’t factoring this in, your recipients probably don’t see what you want them to see:
Email marketers can get around this safety measure if they are Goodmail Certified. If you pay for certification, your images will always be on (for some ISPs). For more information about email certification, check out this article in the MailChimp Resource Center.