Yahoo Mail needs to reach ipv6 target addresses or it will be gone!
Make your email product future ready. Today I cannot send perfectly legitimate e-mails unless the target address runs it's smtp server on an ipv4 address, which is most likely not even the majority of email servers worldwide. And pretty soon there will be no ipv4 smtp servers left on this planet. What then? Yahoo Mail will be gone?

Hi there,
I'm sorry to hear you're experiencing this issue and I'd like to look more into it to help, please contact us on Twitter at @YahooCare or on Facebook at our Yahoo Customer Care page. If you do not have a social media account, we are available at help.yahoo.com through the ''Contact us'' link.
Thank you,
Yahoo team
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Frank-Michael Fischer commented
@YahooCare referred me to you, actually. It's in your court now I think.