SPF and DKIM records willl help... also a dedicated IP that is whitelisted with yahoo would help as well...
Exactly what we offer in our new service..
I figured I'd post and let anyone who was interested know that I was now offering email friendly web hosting...
No spam allowed of course, very strict on that... It also comes with a bit newer autoresponder than Listmail but you should also be able(?) to use listmail if you wanted...
Here's my shameless plug for it:
http://www.extremeleadprogram.com/extreme-autoresponder-realtime-web-host