In the drag-and-drop editor you will find a content block that supports easily pasting in code from another system. For example, you can include Liveclicker elements for real-time personalization, or Ad Tags to display ads within your email. Simply add a row, assign it as the code type then paste the HTML into the box.
iframe code is not supported in email, therefore it will not be supported in the drag-and-drop editor. Once the Design step is passed, the iframe code will be stripped upon save.