Ahh yes got it attaching the graphs internally by following that link to the docs 
My LibreNMS isn’t public so the graphs won’t appear in emails outside the installation which is a bit of a downside. Cacti/Grafana and a few others seem to use some kind of image attachment and cid embed. By attaching the image it would up the mail payload but be accessible anywhere. I saw a related thread here Embed Graph in Alert Email
I don’t suppose anyone has got that working?