I noticed something about my own email reading behavior recently. I've been regularly clicking the "Always show images from SomeAddress@SomeDomain.com" link in Gmail. I get a lot of marketing email from places like Pottery Barn Kids, Travelocity and Barnes and Noble that I haven't bothered to unsubscribe to. I guess the occasional well-targeted ad doesn't bother me. I don't read them, but I sometimes see them as I'm clicking "Next" to page through my unread mail. When I get the imageless version, the formatting is usually so bad that I can't even scan it. There is no hierarchy, no alignment, no attempt at simple design rules that would make it something that I would want to look at.
It would be unfair to say that all of these messages are bad. I get messages from Marriott about special rates, and it includes a well-formatted (but image-free) table that I can glance at without being offended. It's positioned in the email in such a way that it draws readers in and gets the information across easily. For this particular email, I haven't felt the need to see the images because it's so readable without them.Here's an idea, direct e-marketers: pay attention to your non-image emails so that when email systems (prudently) strip out the images, your would-be customers get some kind of message. The "if we can't do images then we don't have to design" approach just falls short, I think.
