Looks like it is even more widespread than Yahoo and AOL. Here is a message from a different mailing list (the Birding lists digest).
"It's come to my attention that around 285 of our subscribers are bouncing all messages from YAHOO subscribers. A little research has turned up the reason: YAHOO has implemented a new email policy called "DMARC" that, in short, is 100% incompatible with mailing lists. Yahoo is aware of this incompatibility, but apparently does not feel that it is their problem. Instead they leave it up to mailing list software developers to figure out a way to comply with the new policy, but apparently there is no clear way to do what a list server needs to do that would comply. Which is probably why the best suggestion the makers of LISTSERV software can come up with is to simply block all YAHOO addresses from posting! We have quite a few subscribers from YAHOO (127 to be exact), so I don't intend to do it if I can help it. But YAHOO users need to know that if they want their posts to reach everyone, they'll have to subscribe and send their mail from a non-YAHOO address. I know that's a hassle, but until either YAHOO backs down or the software company comes up with a fix, there is no other option. (In a pinch I guess you could send your email to a friend who's not on YAHOO and have them post for you, but that's obviously not a long term answer). In addition, all subscribers should be aware that they may not be receiving every post. YAHOO users are of course not getting the YAHOO posts, but neither are users at AOL, HOTMAIL, SBCGLOBAL, and several others. Even personal domains may be affected if they are hosted by one of these services. "
