I tried sending email, but can't and received messages like these, "451http://www.spamhaus.org/query/bl?ip=66.221.112.xxx", what's wrong?

The Cause:

This is a common problem encountered by users who do not have dedicated IP addresses when accessing the Internet. Most users subscribe to an ADSL or cable service with dynamically assigned IP addresses. So, each time you turn on your modem, an IP address is dynamically assigned to you. To conserve resources, ISPs recycle these IP addresses and assign it to the next person who signs on to the Internet. Imagine if the person who has been using that IP address to access the Internet had been spamming (or whose computer has been compromised by viruses) and got his IP blacklisted y antis-spam lists. When you happened to be the next person assigned this blacklisted IP, naturally, your email will be prevented from being sent out.

The Solution:

While you could take up this issue with your ISP, that would be a time-consuming process. Generally, blacklisted IPs get delisted from anti-spam lists after 24 to 48 hours. Instead of waiting, simply turn off your modem for at least 60 seconds and turn it back on. This action resets your modem and should cause your ISP to dynamically generate another IP address for you. Unless this new IP address is also blacklisted (whose probability is rather low), you should be able to send out your email without problem.