The cause for these errors seems to have be some new and tighter spam filtering policies recently put in place for inbound mail messages. Like other ISPs Yahoo’s systems are continually monitored and tweaked for performance. After receiving several notices from mailers Yahoo’s team worked to diagnose and resolve this issue, returning delivery rates to normal – for most mailers. For those of your still having problems, you should contact Yahoo through their postmaster forms at http://postmaster.yahoo.com/
In other Yahoo news; the Email Standards Project has announced some changes in the Yahoo mail client which bring both of the Y! webmail clients into full compliance with their Acid Test. Original Test results.