MailChimp is a pretty common and safe method by which you can sign up visitors to your site and send them newsletters; however the default code doesn't work with DotNetNuke...
So, what we've done, is created an alternative action that DotNetNuke does accept (we've also reduced the signup for MailChimp to a single line... and we've changed the default font to "Arial").
Here is the code, which can be embedded into the editor's HTML in any DotNetNuke portal. Replace the values in RED with your MailChimp embed code... then copy the code below, and paste it into Notepad and then paste).
<table style="height: 20%;">
<td colspan="1" style="height: 20%; text-align: center; vertical-align: bottom;"><span style="font-family: Arial;"><span style="color: #1f497d;">Sign up for our Newsletter!</span> <input type="email" name="EMAIL" class="email" id="mce-EMAIL" placeholder="email address" /><input type="submit" value="Sign up" onclick="this.form.action='http://YOURACCOUNTNAMEHERE.us11.list-manage.com/subscribe/post?u=XXXXXXXXXXXXXXXX&id=XXXXXXXXXX';this.form.submit();" name="subscribe" id="mc-embedded-subscribe" class="button" /></span></td>