I received that email as well. And immeadtily it stood out. Even though FastSpring doesn't have that much of "quality brand design" – but it was still out of place.
BUT – I emailed their support and receievd a reply from "support@fastspring.com" confirming that it is in fact a valid email and I must pay via fastspring link or else our account would be terminated. WTF????!?!?