Delivery Issues

I have noticed that Yahoo is blocking my mailing list again. I’m not on any blacklists. When I send the test mail, it gets through just fine. When I send out the full list, I don’t receive anything. Is there a big difference between how the test mail is sent and how the overall list is sent? I know the list is going out because I receive it in my comcast and gmail, just not the yahoo one. (this has annoyed our YAHOO mail subscribers for awhile now).

Thanks for any input you can give,