WARNING: Mail from our server to some Yahoo email addresses is bouncing. If you need to signup or do a password reset, you may not receive your email from the server. Contact Yahoo support to ask for assistance.
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 - 18.104.22.168; 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.