While legitimate mirrors of email services are rare, fake mirrors are common phishing traps. They are designed to look exactly like the Yahoo login page to harvest your username and password. Always check the URL in your address bar. If it is not yahoo.com , mail.yahoo.com , or a regional variant you recognize (like yahoo.co.uk ), do not enter your login details.
This is the most common scenario. System administrators at schools and workplaces often configure firewalls to block specific categories of websites. Yahoo often falls into the "Webmail" or "Entertainment/News" categories, which are restricted to prevent procrastination or preserve bandwidth. In some cases, specific URLs like yahoo.com/mail are targeted to ensure employees or students focus on their tasks.
: To mask the destination URL from simple filters.