Spam & Virus Filtering
Spam Filtering services
Spam is a growing problem, heading toward becoming a global epidemic. Interestingly, contrary to popular opinion about China & Korea, the no. 1 country
from which spam originates is the US. In some ways it makes sense.
There are currently a number of methods for combating spam:
- RBLs ("Real-time Blackhole List") or DNSBLs ("DNS blacklist"). These are lists of IP addresses of email servers that are open relays being used by
spammers to distribute spam. Because securing a mail relay is relatively simple, these mail servers are considered to be spam-friendly. Owners of mail servers
then subscribe to these lists and actively reject connections from mail servers on the list.
- Signature based filtering. This is a text based filtering system that looks for patterns within the message itself, and matching it to known patterns.
Most of these systems use spam scores to decide if an email is spam or not, with normally more than one matching pattern contributing to a failing score. Spam filters
also use Bayesian filtering. These filters must be trained before they are effective.
- White listing. White list filters basically say "Any sender not on my white list is a spammer". This is not as harsh as it may first appear.
Most of these white list filters monitor outbound email and automatically add the email address of the recipient to the white list. Users within a company using this system
will have the opportunity to manually add safe senders to the white list. An additional feature often added to the white list filter is an automated system that replies
to an email blocked as spam asking the sender to resend within a specified time. If they do so, the email is allowed through and the senders address added to the white list.
Spammers never send from their own address!
Spam filtering is somewhat of an art form, and spammers are constantly probing for holes in current defenses. A lot of time can be spent combating this social scourge.
Spam filtering is traditionally handled at the border, and there a number of effective open source solutions (SpamAssasin
for example) which work well on Linux, as well as some very effective commercial systems. Mail Marshal is very popular within New Zealand.
It runs on Windows and is very easy to administer.
Microsoft Exchange also offers interfaces to plug spam filtering services in to the Hub Transport layer. This would catch spam even within the corporate network!
I am experienced in all these systems, including writing the regular expressions found in pattern based systems. I can guide you through these murky waters, please contact me to get started
on your anti-spam system. Alternatively, we can discuss anti-spam services.