By default, MassMailer adds an unsubscribe link at the bottom of the email. If you are looking to custom position the unsubscribe link in your emails, you need to follow the instructions below.

In your Email Templates in Salesforce, you can add the replacement tag, "[unsubscribe]" in your HTML code in any position just by adding it as the 'href' attribute value for the anchor tag.

<a href="[unsubscribe]">click here to unsubscribe</a>