I have "recorded" a lot of different domains pointing to yahoo MXs.There are the ones missing from your list and for which I recorded opens in the last 2 months:yahoo.clyahoo.co.jpyahoo.co.thyahoo.com.coyahoo.com.myyahoo.com.tryahoo.com.veyahoo.com.vnyahoo.inyahoo.nlyahoo.noyahoo.plyahoo.rothose domains IMHO are yahoo domains (like rocketmail):bakuoilservices.combbh-systems.combook-tokyo.comcitlink.netfrontier.comfrontiernet.netmadselectronics.commawicoffee.comnl.rogers.comodosupo.comrogers.comsky.comtracygirdler.comxtra.co.nzy7mail.comybb.ne.jpI don't have opens from yahoo.com.cn (the only one from your list).There also a lot (thousands) of minor domains that points to a "biz" mx, so I guess they are hosted by yahoo, too.
You forgot pacbell.net, bellsouth.net, sbcglobal.net, ymail,com, rocketmail.com, ameritech.net, att.net, flash.net, nvbell.net, prodigy.net, snet.net, swbell.net, wans.net.These are all email domains Yahoo hosts for AT&T companies.
It is true that AT&T users have the ability to use Yahoo webmail to read their email. But, the AT&T domains have separate MXes and separate spam filtering. It's possible to be blocked or bulking at Yahoo but not at AT&T. So I likely would not put them in the same category.
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