In our continuing efforts to protect our users from unsolicited email, Yahoo! Mail does not accept SMTP connections from dynamic or residential IP addresses, as determined by the Spamhaus PBL. If you are seeing this error message, please do not retry sending your message using the same IP address. Instead, please contact your ISP for information on which SMTP server you are authorized to use for your outbound email.

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