The EEC and SubscriberMail, the sponsor of this study, surveyed 472 marketing executives in March and found that 23% of the e-mails from this study were completely unreadable in an inbox environment. In addition, only 47% of the survey respondents said that their company had taken action to help with image rendering.

“For most b-to-c companies, HMTL e-mails are still considerably more effective than text-only e-mails, so marketers are right to design their e-mail with images,” said Chad White, director of retail insights and editor-at-large for the EEC. “However, many e-mail clients and ISPs now block images by default because of concerns about image-based spam.”

There are a number of things that marketers can do to make their e-mails readable when images are blocked, according to White. Using alt tags, designing e-mails with as much HMTL text as possible, and using a preheader text could work.

“They can also ensure that the images in their e-mails render by encouraging subscribers to whitelist them during the sign-up process and in their welcome e-mails,” White added.

Interestingly, 42% of the 104 top online retailers included in the study are designing e-mails that were “a good mix of HTML text and images,” and only 63% used alt tags, a technology that helps with image reading.