tried sending email, but can't and received messages like these,
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.
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.