The reason for the problem:IP address 18.104.22.168 is for smtpout.karoo.kcom.com which is one(?) of the Eclipse email servers.
4.3.2 - Not accepting messages at this time 421-'4.7.0 [TS01] Messages from 22.214.171.124 temporarily deferred due to user complaints - 126.96.36.199; see http://postmaster.yahoo.com/421-ts01.html'
I don't get this delay report for any other emails. Is it an Eclipse (KCOM) problem in that their server is being reported as a spam server, or a Yahoo problem for falsely seeing the server as a spam server?
And, if it's an Eclipse problem, why would other email servers not be aware of it and delay similarly?