Using Classic Outlook on Windows for personal email, calendar, and contact management
S**t! One of the changes we made to my account involved the SPF record, and now it's fixed. We also made changes to the DMARC records.
I like your theory of an enforcement change at Yahoo. Even so, refusing the socket hardly seems like the correct response to an SPF failure.
Agreed that the response seems incorrect. I suppose they are more interested in foiling spoofers, so dropping the socket connection is the easiest thing to do. Not that I agree with it, just that it makes sense.