This was posted today...

tech.groups.yahoo.com/group/ymailadmin/message/17

If you're seeing some queuing in your outbounds today when sending to Y! users, we're currently experiencing low connectivity across our MTAs, which started this morning. We're working to get things back to normal.  The SMTP error message being generated by the issue should be:  "420 Resources unavailable temporarily. Please try later hostname>" Our apologies for the inconvenience.