Get whitelisted. This ensures selected email is allowed through the system with minimum filtering, image blocking included. If a user adds the sender’s address to her address book or "safe list," the email is untouched by most ISP and personal filters.
   

Add a "view Web version" link. Host a version of your message on your company’s Web site. Provide a text link to it at the very top of your message. Regardless of image or personal settings, the recipient can always click through and view the message as a Web page.

Check message appearance in the preview pane. Can recipients
make a quick "open" decision based on content showing in the preview
pane? If not, consider reformatting the message or adding teaser text
at the top that highlights key message content.
   

Include alt tags. Although many email services and email
clients don’t display alt tags when images are disabled, it’s always a
good idea to include them. Regardless of why, if images haven’t loaded,
properly written alt tags may provide the recipient with enough
information on which to act.
   

Use text-based ads. Publishers carrying server-based ads
might consider including more text-based ads. Coincidently, some
publishers report text ads deliver higher CTRs (click-through rates)
than image-based ads.
   

Create text versions. With HTML email so popular, text
versions tend to be neglected. Yet recent email client changes mean
users have an increased ability to select which default format they
prefer. A strong text version ensures you still reach users, regardless
of format preference.
   

Include more text links. If your email includes several key
linked images, consider adding text-based links above or below the
image or appropriately placed in nearby copy.
   

Focus on CTRs and conversion rates. Don’t obsess over open rates. Monitor CTRs and conversion rates and focus on maintaining or increasing them.

To read more about EmailLabs’ perspectives on Image Blocking, visit: www.clickz.com/experts/em_mkt/email_delivery/article.php/3413471

Source: EmailLabs