Smart Creative was recently tasked with tackling some last-minute communications to help get the troops from the American Advertising Federation to the Rally in Tally - the industry's chance to say our peace with legislators at the Florida capital. The chosen tactic was eblasts, and I thought this might be a good chance for a quick discussion on what makes for effective advertising with those sometimes spammy little mass messages we get.
Personally, I like to approach an eblast as I would a billboard or a poster. Few words, quick messages, strong contrast, and easy-to-understand concepts.
Light backgrounds allow for breathing room inside a viewer's email box (but dark backgrounds can create super-cool framing opportunities).
I prefer something that can be converted to a GIF because it'll keep the file size down, which means I tend toward illustrative pieces as opposed to photographic. These three different blasts ended up about 16k each, which is tiny.
Overall advice, though, is to provide memorable imagery and a clear call to action. That's how you'll get the best response rates.