If you are about to send out an email to your members and have a Yahoo email address as the 'Sender', not all email servers (Gmail, Hotmail ect) will receive your communications.
This is because email’s sent with a @yahoo.com email address do not essentially originate from Yahoo itself, and are therefore not sent from a Yahoo email server.
This results in other email servers blocking or bouncing the email by DMARC complaint receivers. Yahoo implemented this change to prevent increasing email forgery and spam.
In basic terms, if you send an email to your members with a @yahoo.com email address, some of your members may not receive the email.
The solution is to change the originating 'Sender' email address to non-Yahoo email account.
See below sources for more information:
https://help.yahoo.com/kb/mail/SLN24016.html?impressions=true
http://yahoomail.tumblr.com/post/82426900353/yahoo-dmarc-policy-change-what-should-senders