since (apparently) I can't access the correct yahoo-help channels I just wanted to inform you, that recently I got Emails from a Yahoo-account to another Yahoo-account rejected due to DMARC-issues!? How can a user resolve issues if you don't trust your own servers-?? Here is the rejection message:
*** SMTP error from remote mail server after end of data:
554 5.7.9 This mail has been blocked because it failed authentication checks against the sending domains DMARC policy. ***