Eloqua makes it possible to send radically different versions of an email by using the Dynamic Content functionality.
Sometimes there is a use case that the default setting needs to be BLANK and collapse the email so the BLANK space doesn't appear.
To be sure the content collapses completely, you need to use the HTML email editor rather than the WYSIWYG. You still create the dynamic content in the same way by using the Eloqua dynamic content option from the left navigation. But the default section needs to remain completely blank. You don't need to add any code whatsoever.
You then add the various rules need to make the content dynamic and then drag the content blocks into the source where they need to be added.
It's highly recommended that you preview the various possibilities to make sure the rules are applying the way you need them to and that the email is collapsing correctly. The system works surprising well for something that seems is complicated. Most likely if there is a mistake, it's because your contact data is bad.
My experience is with E10.