All email campaigns sent from MailChimp must include our *|UNSUB|* unsubscribe tag. When MailChimp delivers your campaign, he'll replace that tag with your list's unique opt-out link. You can alter the text in your footer, but don't ever remove the *|UNSUB|* tag or remove your address (you can manually add it if you do not want to use the system tag). Here's some sample code you can use for your plain-text emails:
Copy-paste this into your plain-text email:
================================================== Unsubscribe *|EMAIL|* from this list: *|UNSUB|* Our mailing address is: *|LIST:ADDRESS|* Our telephone: *|LIST:PHONE|* Forward this email to a friend: *|FORWARD|* Update your profile: *|UPDATE_PROFILE|*
You can probably tell what all the little *|MERGETAGS|* will be replaced with, whenever you send the campaign to your list. Just make sure that your list has all of that information entered (it's all under your List > Settings under the "required email footer content" area).
Feel free to edit the content any way you want, but remember: don't remove the *|UNSUB|* tag or your address.