Thanks for asking.
The domain to which mail is going is prodtoolcorp.com.
We are aware of issues when email is sent from Yahoo or AOL. (Likely the same issue, since those two services appear to have the same back end.)
To our knowledge, no other organizations are having this issue.
Prodtoolcorp uses a Barracuda spam filter solution. The message log in the Barracuda shows NO emails from Yahoo, at all. Any emails that get processed by the filter appear, whether discarded as spam, quarantined, marked [BULK], blocked, delivered, or whatever. The Yahoo and AOL emails never appear in the list. The really, really weird part is that when there is a rejection email, which does not come back to Yahoo senders, it comes from Barracuda Networks saying 'domain not found', when we can email that domain successfully all day long.
How the exact same spam filter can consistently tell one sender a domain isn't found, yet let another deliver makes no sense to me. I will be talking to Barracuda, but had wanted to hear from Yahoo what message resulted from trying to send, but there is nowhere I can find where that information can be had.
Yahoo 'support' is a bad joke. And that was in no way a criticism of you.
As to Yahoo mail server IP addresses, I have not tried extracting every IP address from the server logs and compared each of them to the dozens and dozens of IP addresses listed at the page to which your link connects.