I am getting a lot of mail to Yahoo domains rejected at the moment, with the error message that mail is: "temporarily deferred due to user complaints - 4.16.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html" However, the only mail to yahoo users will be from sign-ups to the website... So I dont know what there is to complain about. If you want to join the site and you use Yahoo, please contact support, and ask them to fix their mail server.