Yahoo change can break mail lists

Oops.

If you have a mail list set up so that any replies go only to the person sending and not to the list -- and if you have any Yahoo addresses -- a Yahoo policy change could cause you some problems.

See http://yahoomail.tumblr.com/post/82426900353/yahoo-dmarc-policy-change-what-should-senders-do

For a more technical explainer: http://www.computerworld.com/s/article/9247512/Yahoo_email_anti_spoofing_policy_breaks_mailing_lists?pageNumber=1