Hi,
Yahoo has an annoying habit of making life difficult for mail admins, and they have recently done so again by enabling a DMARC 'reject' policy for all of their subscribers. DMARC is one of the newer tools to combat spam, but it has the unfortunate side effect of being completely incompatible with most mailing list software. This came to my attention this morning, when most of the yahoo subscribers to the mailing list were disabled.
http://yahoomail.tumblr.com/post/82426900353/yahoo-dmarc-policy-change-what-... http://wiki.list.org/display/DEV/DMARC
I have this morning upgraded the Mailman software used on the Xymon mailing list. The effect of this is that mails from Yahoo adresses (and others, who has set DMARC policy to 'reject' or 'quarantine') will be wrapped in an "outer message" when forwarded to the list. Most of you won't notice, but it depends on how your e-mail client handles such messages.
Regards, Henrik