In our continuing efforts to protect our users from unsolicited email, Yahoo! Mail does not accept SMTP connections from IP addresses of compromised machines, as determined by the Spamhaus XBL. If you are seeing this error message, please do not retry sending your message using the same IP address. Instead, we encourage you to take steps to secure your machine (e.g., update and run anti-virus software), along with any other machines on your network.

If you think that your IP address has been listed in error, you or your email administrator should contact Spamhaus. Once your IP is delisted by Spamhaus, Yahoo! Mail will automatically unblock your IP within 48 hours.