Image density definitely affects the delivery of emails.
If there is more imagery than text in your emails, it will absolutely hit the spam folders, so getting the balance right is incredibly important.
So even though you may want your emails to be branded with lots of incredible colours, lots of pretty pictures, lots of charts, lots of tables, and a lot of performance numbers, it is wise to know that if the imagery supersedes the amount of text you are putting in your email, you are in harm’s way of being tagged as SPAM.
We at ProFundCom have found a correlation between the number of people who physically tag emails as junk, and the number of images. The reason people get image density wrong (and even ignore it) is a lack of understanding of what may look great on a designer’s screen, and what may actually be prime to be tagged as SPAM. And why not – after all if you send a brief to a graphic designer all they want to do is show you how brilliant they are. And you are equally culpable by looking at something and saying, “Wow, that looks amazing,” without caring about deliverability!!!
As far as the inbox is concerned, an inbox doesn’t care.
Inbox cares about image density, so getting that right may mean reducing the design element of the email.