There are several ways to get a gray bar or default footer added to the bottom of your campaign.
Reason Number One:
As part of our Terms of Service, MailChimp requires all campaigns to include our unsubscribe tag. If you have removed this unsubscribe tag, or altered the provided Templates in a way that doesn't allow us to auto-populate the footer area of your campaign, we'll place the default gray bar with the footer information automatically at the bottom of your campaigns.
If you want to use the gray bar, you can simply delete the text in the main footer area, so that your footer information is not doubled.
If you want to get rid of this bar, add the unsubscribe tag back into the main footer as described in this article.
Reason Number Two:
If you have a free account AND are providing your own HTML code, you'll need to add the *|REWARDS|* tag into your HTML email. That will add the required MailChimp logo on your campaign. If you don't have the *|REWARDS|* tag added to your HTML, we'll automatically place it on your campaign via the gray bar.
Reason Number Three:
If you have very complicated code (like content brought over from Word) or broken code, it's possible that the browsers can't make sense of the code and thinks this is indicative of someone trying to hide the unsubscribe or rewards link/tag. The most common cause of this is a comment tag in your code that does not have a corresponding closing tag. You're probably NOT trying to hide the link, but in the case of something odd in the code sometimes the browser isn't sure what to think. If it's not reasons One and Two that are causing the problem, check out the code you've used. There could be something there causing the extra bar.