The design of the elements in an email campaign can dramatically alter click-through rates. As can be seen from the image below, we scan the pages we read in a "F" pattern. As a result, it makes a lot of sense to incorporate the messages we're looking to promote into the areas of an email that are read the most.

With Business-to-Business email newsletters, it's the content that'll engage the audience the most that should be placed within the "F". This is in contrast to Business to Consumer marketing where you'd want to have advertisements and offers.

Separately, I've heard that using the same blue as the Google search page (#2200CC) increases click-through rates but we've not finished testing that (yet).