I keep getting bounce warnings from this list, apparently because of a problem with Yahoo. The bounce messages say, "host gmail-smtp-in.l.google.com[18.104.22.168] said: 550-5.7.1 Unauthenticated email from yahoo.com is not accepted due to domain's 550-5.7.1 DMARC policy. Please contact administrator of yahoo.com domain if 550-5.7.1 this was a legitimate mail. Please visit 550-5.7.1 http://support.google.com/mail/answer/2451690 to learn about DMARC 550 5.7.1 initiative. ro6si3093371igb.36 - gsmtp (in reply to end of DATA command)"