Microsoft updated the SPF record for hotmail.com in the last 24 hours but forgot to keep their IPv6 addresses in it, so as a result places all over the world are rejecting emails sent from Hotmail as forgeries.
EDIT: Removed my comment about not rejecting for SPF failure. Microsoft are requesting rejection of their own email here (-all).
https://www.reddit.com/r/sysadmin/comments/15u28tw/microsoft_seems_to_have_broken_spf_for_hotmailcom/
#IPv6 #Hotmail #Microsoft #SPF