According to this email, which purports to be from Yahoo, your account has security issues and you must therefore click an “Authentication Page” button to visit your account and deal with the problems. The message warns that, if you have not completed the authentication process within 48 hours, you will be blocked from sending and receiving emails.
However, the email is not from Yahoo. It is a typical phishing scam. If you click the button in the message, you will be taken to a fake website designed to closely mirror a genuine Yahoo webpage. The fake page will ask you to enter your Yahoo ID and password. Once you have “logged” in, you will be redirected to the real Yahoo website.
Meanwhile, the scammers can collect your login credentials and use them to hijack your Yahoo account. Once there, they can use the hijacked email account to send spam and scam messages that look like they were sent by you.
Scams like this are very common. Be wary of any unsolicited email that claims that you must rectify an account issue by clicking a link or opening an attachment and providing login details or any other personal information.