|
Spam Prevention
Directory Harvest Attack (DHA)
A Directory Harvest Attack (DHA), is when the
spammer sends spam to every conceivable name at your domain. You can
prevent these attacks by rejecting email sent to a non-existent user.
Tarpitting
Tarpitting discourages Directory Harvest
Attacks without permanently blocking an offending IP address by slowing
down incoming email from that address. Our mail server waits two seconds
before responding to an invalid recipient command.
Denial of Service (DoS) Attack Protection
If we receive "x" number of connections from a
given IP address in a single day, we defer future connections from that
IP address for "x" number of hours.
Bounced Address Tag Validation (BATV)
Bounce Address Tag Validation (BATV) reduces
the number of unauthorized NDRs (Non-Delivery Reports) delivered to your
organization.
Spammers commonly forge sender email addresses when sending spam in
order to make the spam email look like it was sent from a valid email
address. If that spam cannot be delivered, an NDR is sent to the forged
sender's email account.
BATV protects your organization by adding a signature to all of your
outbound email. When an NDR arrives at your organization, BATV is used
to check for a valid signature. If the signature does not exist or does
not pass the security check, Email Security rejects the NDR. If the
signature is authentic, the NDR is valid, and Email Security continues
analyzing the NDR.
Greylisting
Greylisting discourages spam without
permanently blocking a suspicious IP address. When greylisting is used,
your Email Sever assumes that all new IP addresses that contact it are
suspicious, and requires those addresses to retry connecting before it
will accept the email.
Throttling (Flow Control)
When using "throttling", if the mail server
receives "x" number of invalid emails from a given IP address, it defers
future connections from that IP address for "x" number of hours.
All of the above
techniques work very well for us. We have found that fighting spam requires
multiple approaches to be extremely effective. As a result of our having
posted our email addresses on the internet since 1996, we have fallen victim
to those automated email address harvesters and probably appear on many,
many spammers' lists.
The fact that
our addresses have been exposed for so long, coupled with our active role in
fighting spam has made us a target of the spammers.
|
|
