Hi,
It seems it is not stated in the docs. Here is what I could find on that topic:
By default you need to have the templates in /content/campaigns, this call is made from AC to AEM:
/api/content/sites/campaigns.json?query=SELECT%20*%20FROM%20page%20WHERE%20%5Bchild%5D.%5Bcq%3AacLinks%5D%20IS%20NULL&limit=30&filter.rt=mcm%2Fcampaign%2Fcomponents%2Fnewsletter%2Cmcm%2Fcampaign%2Fcomponents%2Fcampaign_newsletterpage%2Cmcm%2Fneolane%2Fcomponents%2Fnewsletter&showAllProperties=true
However if you put a rewrite rule (Apache) in place, you can transform the call to this:
/api/content.json?query=SELECT%20*%20FROM%20page%20WHERE%20%5Bchild%5D.%5Bcq%3AacLinks%5D%20IS%20NULL&limit=30&filter.rt=mcm%2Fcampaign%2Fcomponents%2Fnewsletter%2Cmcm%2Fcampaign%2Fcomponents%2Fcampaign_newsletterpage%2Cmcm%2Fneolane%2Fcomponents%2Fnewsletter&showAllProperties=true
This then gives you templates located in /content.
Let me know if that's something you could do. Otherwise you'll need to have the email templates somewhere under content/campaign.
Florent