Trying to send my first e-newsletter with the Mosaico system
Sending of CiviMail requires both the domain.address token and the action.optOutUrl or action.unsubscribeUrl tokens

You can add these in to the bottom of your mailing. Add a text block, add the above tokens, then edit it by clicking on &lt; > (source code) and put a link on to the optOutUrl token with the destination also being the token so it ends up like 

&lt;p&gt;{domain.address}&lt;/p&gt;
&lt;p&gt;&lt;a href="{action.optOutUrl}"&gt;{action.optOutUrl}&lt;/a&gt;&lt;/p&gt;


There are some longer instructions here I wrote up yesterday. They may help