Having managed a number of largish email systems over the past few years, I've got to say that dealing with Yahoo -- DKIM and other anti-spam related issues -- is one of my larger ongoing headaches. The lack of response and transparency of Yahoo in general is a huge problem -- I managed to get resolution in one case via an executive email carpet bomb (this after repeated contacts with their support team and direct emails to the CTO/Postmaster's address).
Sadly, as much of a fading giant as Yahoo are, their email presence remains huge.
Postmaster address? According to http://rfcignorant.org/lookup/yahoo.com (and from personal experience), Yahoo do not have a postmaster address. If you want to report a problem, you need to find a deeply-buried form somewhere on their web site. Oh, and if you don't have a Yahoo account, you're out of luck, because you need to log in to use that form.
I'd emailed Raymie Stata directly. Never, ever, got a response. Contrast with Microsoft: I dialed the switchboard, tequsted the EVP in charge of Hotmail, he picked up on the first ring, and I was talking to the relevant manager 15 minutes later who worked with me for a few months resolving the issue.
I'm not a Microsoft fan, but their people were very professional in this case.
Raymie Stata hasn't worked for Yahoo in a long time. You can go here, https://help.yahoo.com/kb/postmaster when you have issues. Was very easy to find. postmaster.yahoo.com
I disagree. I've had Yahoo reject my emails completely silently (didn't arrive in inbox OR 'spam' folder, even though Yahoo's MX said the message was accepted). Yahoo was entirely unresponsive about this issue. We didn't have the same problem with any other provider and it was resolved immediately upon switching to a third-party email delivery service.
Additionally, Yahoo has a huge amount of abuse and doesn't seem to have an abuse handle either; you have to fill out some form buried deep on their site. On the other hand, I've reported abuse incidents to Hotmail before and have gotten an actual reply from a human (a rarity when submitting abuse reports; most places act on them but don't bother responding).
In terms of being responsive to issues, I've actually had far better response from Microsoft than Yahoo, as I described above. Call the switchboard, ask for the SVP in charge of the division, get transferred directly to him, he picks up the phone on the first ring and talks for ~10 minutes to hear my issue (spam transiting Microsoft's network). Tells me I'll hear from the manager in charge, who calls me 15 minutes later and works over the course of several months (these things do take time) to resolve the issue and improve their systems.
As I wrote above: I'd written Raymie Stata repeatedly after getting a complete runaround from Yahoo's tech support (and diving into dead ends on their website), never hearing a peep from him. Not until I emailed pretty much the entire C-level suite and senior managers with a bit of data showing the nature of the problem (postfix delivery time stats) did I get a return response, from Yahoo's "concierge" service. That finally resolved the particular issue I was dealing with, but that's one appropriate response in years of dealing with the company.
The resolution with Yahoo was essentially the one described in your Serverfault link: get explicitly whitelisted. That's not uncommon with top-tier email service providers.
Sadly, as much of a fading giant as Yahoo are, their email presence remains huge.