Backgrounds images can enhance the look and feel of your templates but nowadays they should be limited, or avoided. The main reason is pretty simple: many email clients ignore images or do not render properly the background-image style tag.
It means that if you choose to include them in your HTML emails, a portion of your subscribers which are using readers like Microsoft Outlook 2007 and Gmail, will not display them and so they will not get the same “experience” as others.
If you still want to add background images:
– make sure to use absolute paths for your code
– use the background= attribute in the TD cell or in a DIV, instead of using CSS.
– apply a background color to provide the same color styling as the background image, to allow recipients who cannot view the images to see the bg color instead.