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Computer Log 28

Well today I am going to talk about e-mail Spam and several of the ways it is block by an e-mail server. This Computer Log will require your propeller hats to be put on. Spam is usually forwarded by compromised Windows Based home computers and rogue mail servers instead of standard mail servers. We who run e-mail servers either for businesses or for end users are always trying to find ways to limit the Spam. Many mail servers use a combination of virus filtering and Spam filtering by using Real-time Blocking Lists or RBL's as we say in the trade.

RBL's are list of addresses that are sources for Spam and the different list out there will filter different types of Spam. Some RBL's will actually cause legit e-mail to be block due to there aggressiveness, or if the e-mail is using a server that is actually passing Spam. This is what I have to consider when using RBL's . I use the DNS methods of RBL's due to the fact I do not have to put a heavy load on my server nor use up a big piece of bandwidth in order to use the RBL Lists.

Most e-mail servers can use a number of RBL's so the mail-server and address a number of Spam attack vectors. I have been fighting Spam for years and using RBL's with the understanding that this is not a cure all for this problem. I have seen local servers get blocked due to issues caused on their network.

Each RBL will block a specific type of Spam generator. One will block a specific countries IP address block like North Korea's. Another will block an IP address that is passing infected e-mails, while another is blocking IP addresses that should not send mail directly, like a mail-server from a dynamically obtain IP address. A dynamic IP address like most cable modems and some ADSL modems all depending on who you use to go online. And even another RBL will detect open relay mail servers.

An open relay mail server is where you can send e-mail without authenticating and relay your mail to another server. Most good ISP's and most hosting companies will require authenticating your outgoing e-mail. Both G-Mail and Yahoo Mail requires authentication of one sort or another. Authentication can be anything from using a specific set of IP addresses to allow you to send e-mail to using a specific login name and password to send e-mail. A Webmail interface is one method.

Some of the ISP's or Mail Server companies will do word filtering and if you hit this due to the way you write an e-mail, it can be a big pain. So far as I have seen, only swearing, and porn references have been used to filter e-mail.

Using RBL's is a balancing act and if you do not keep an eye on the RBL's you use, can give you gray hair from complaints of your customer base, and at my age I do not want gray hair. RBL's will update themselves hourly or daily depending on the method they use to determine a Spam source.

For more information check out this link:

Franklin S Werren is a Computer technician and runs Chautauqua Lake Hosting and Franks Radio in Sherman ` NY. And can be found on the web at , and , also via e-mail at

Disclaimer: Neither “Franklin S. Werren” or the “Chautauqua Star” have received any money or promotional items in anything talked about in this column.

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Page last modified on June 30, 2010, at 05:46 PM EST