Just noticed that there were replies to several inquiries where I missed the original message.
Checked the Yahoo SPAM folder and found a ton of messages that got caught in their blacklist. Including one from myself! Most were in the last couple days. But there was a line one from Sunday the 12th. (All have been manually tagged 'Not Spam')
It's easy to miss the 'Move To' icon in the Yahoo! mail GUI and hit the adjacent Spam icon. But somebody who doesn't know how to unsubscribe or use the digests might have marked us as Spam in frustration too.
Yahoo shares their blacklist. So other services might pick up blacklisting this mailing list server. It takes a few days for white & black list updates to propagate.
So I suggest everyone monitor their SPAM filtering systems for a few days.