Customer service email address
customercare@cc.yahoo.com
Forward all of your spam to these idiots, and give them a taste of their own medicine. They won’t respond, but do receive.
50th
ranked

While most of spam emails are being caught by our spam filters, occasionally some can slip through.
When this happens, it's very important to mark the email as spam, then our system will learn that messages from a specific place are not good and helps us make Yahoo Mail even better at recognizing future spam emails.
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Sandip Das commented
Make the spam folder as inbox and inbox as spam folder as legitimate mails are going to spam folder only. I am really fed up with your mail system, yahoo has gone astray I feel.