Same issue here.
I even filled out the form that yahoo suggests we fill in if we want to send email to their servers:
Aside from a standard response saying that they can't guarantee delivery I didn't get anything from them.
My error is this:
150D6125B8B 90331 Fri Jan 16 09:53:14 email@example.com
(host mta5.am0.yahoodns.net[18.104.22.168] said: 421 4.7.1 [TS03] All messages from 22.214.171.124 will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html (in reply to MAIL FROM command))