Experts
say unsolicitited e-mails (SPAM) constituted over half of
all e-mail messages sent. How others deal with this problem
affects you whether you know it or not.
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SPAM:
Blacklists & Whitelists
Spam. Anyone connected to the Internet has heard the word. Anyone
who has an e-mail account dreads the word. It has been estimated
recently that one third of all e-mails transferred from computer
to computer are unsolicitated: i.e, spam. But rather than talking
about the generalities of spam this article attempts to inform
you of two methods used by companies to combat spam and how
they may affect you. These two methods are called Blacklists
and Whitelists.
As the name suggests Blacklists are lists which exclude something.
In the case of spam Blacklists exclude IP addresses which are
associated with spam and block all e-mails coming from those
IP addresses. But how does a Blacklist affect you? Before you
can determine how this affects your web site you must understand
IP addresses and how they work with web hosting.
If you have shared hosting on a server, chances are you are
also sharing an IP address. An IP address is the numerical representation
of where you server is. While humans use alphabetical names to
remember a web site; computers and servers don't know where www.e3servers.com
is but rather know that it is located at 64.191.62.74. The numbers
64.191.62.74 is the IP address of the web site www.e3servers.com.
Whenever a computer needs to contact www.e3servers.com or send
mail to www.e3servers.com it knows that the IP address is associated
to that domain. Now, www.e3servers.com is not the only domain
(or hosting account) using this IP address. With the aid of server
software a single IP address can be reused by more than one domain
at a time. This is called virtual hosting. There are many reasons
why several domains may be using the same IP address but realize
that tens or possibly hundreds of domains may be sharing the
same IP address on a server. Now let's examine why this is important
when talking about Blacklists.
When a spammer sends out spam, either through a hosting account,
or through exploiting a security hole in a server the e-mails
are sent from a hosting account which has an IP associated to
it. When other computers, and users, find out that they have
received spam and they trace the unsolicited e-mail back to the
domain which sent the spam. What happens next is that this IP
address, which is associated with the spam, is now listed as
sending spam and is listed on a Blacklist. What happens next
depends on the people running the Blacklists the IP was just
listed on.
Blacklists can be characterized as three different types: the
temporary, the permanent and the obscene. Before the differences
are discussed let's talk about what a Blacklist does: a Blacklist
is nothing more than a list of IPs in which all e-mail originating
from them is blocked. Any e-mail coming from a Blacklisted IP
address is returned to the sender without ever reaching the intended
recipient. Now the computers which are using the Blacklists do
not determine what is spam and what is not spam and only block
the spam--they block all e-mail whether it is spam or not.
The differences between the different types of Blacklists is
a function of how the people running the Blacklists deal with
the spam. The individuals running the temporary Blacklists monitor
for spam and when they find spam coming from an IP address they
distribute this IP address to their followers and all e-mail
from that IP address is blocked for a period of time. Usually
this period of time is several hours. The reasoning for this
is that most spammers use an IP address once and then move on
after sending millions of e-mails to the next IP address. The
temporary Blacklists essentially have a rolling target of IP
addresses they block as the spammers move from IP to IP.
Continued
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