JACK THE SPAM KILLER!

ardon my moment of self-indulgence by using the name "Jack" in the title. It is apropos however when considering those very words brought a smile on my face when used in a recent message to me by one of our mail server's email users. I was also urged to publish an article about the subject material, not only in antenneX, but possibly in some applicable ISP Journal as well. I was flattered by the suggestion, of course and feel I should follow through with the idea to share information this month about a problem that everyone reading this has in common to some degree—SPAM.

The message mentioned above was in response to my announcement that our mail server SPAM controls had been enhanced to not only identify as much as 99% or more of the SPAM, but to prevent it from entering the email user's account at all. This means a substantial reduction in the amount of time required to download messages from the email server to the user's local computer. Time reduction is running in excess of 75% by eliminating the existence of SPAM contained within the usual download, even though the SPAM may only have been one-third of the total emails. The time reduction is even greater when one considers that the SPAM emails must still be managed after the download and removed from the email program. But, no longer for users at our mail servers!

BLOCKING
For years, each of our mail servers had maintained a "blacklist" of domains known for being an open relay for SPAM. Our own list contains hundreds if not more than a thousand of these offenders. This special method denies and blocks entry to the server at all so that ANY emails from them bounce off completely. That is using real brute force in that case, but it only works if the domain is used more than once and works even if the domain is not a valid one as long as the domain name is used in the SPAM header. Also, care must be used when adding such names to this list as it can block good emails too if the domain was not aware of its name being misused.

Additionally, we employ the use of other blacklist services that specialize in tracking down the bad guys and maintaining a huge list of this sort. Their list contains thousands of domains because it is their specialty and they are able to dedicate the time required to track and verify a spamming source. Such services are used in real time and every email received is checked against their list in addition to our own blacklist.

However, as one might expect, the spammers caught on to the above blocking technique and started devising tricks to get around the blacklists in their relentless desire to reach into our email boxes. Simply not using the same domain name more than once was one of the most obvious methods to employ, however, it was not enough to use fake domain because server email programs also got smarter and did not accept emails from a domain that could not be "resolved" as being a real one.

FOOL THE SERVER
So, then the next trick used by spammers was to use real domains to fool the server's email program, knowing this created a quandary for the server that would not block a legitimate domain with which legitimate business needed to be conducted. Good examples are the big popular domains like yahoo.com, hotmail.com, msn.com, aol.com, and many more familiar to most, which handles millions of email accounts and most likely hundreds or thousands of incoming emails for various user mail servers. It just would not be practical or feasible to block those domains as they could represent a source of a large percentage of good emails and to lose those could hurt business.

Although, the above trick now made use of real domain names, the user name did not have to be real. No doubt many have seen this trick used where the email sender would be addressed to something as obviously forged as "xyz@yahoo.com."

Ahah! So, the server email programs became even smarter to counter this new trick and the blocking ability was expanded to allow blocking in a new form such as xyz@ and thus without a domain name. This would catch and block any domain using that forged user name.

BAD AND GETTING WORSE
Okay, not unlike any other "war" (and it is a war!), for every action there is a reaction. The bad guys seeing this new form of blocking found yet another new trick to get around server blocks-hijacking real domains and usernames so that you might get an email from someone you recognize and once again be fooled into opening the spammer's message. Once again, this made it more difficult if not impossible to add names to the list because the email address is legitimate and may very likely be one of the server's customers or one of its user's customers. And, this "trick" really created a tremendous amount of confusion for many email users who found themselves wrongfully being blamed for sending out SPAM. This was bad and getting worse.

Just in time, here comes the Calvary! Enter SpamAssassin a very powerful, feature-rich spam-fighting program primarily designed for the mail servers. I have discussed this program in a couple of earlier columns, but since then the program has been enriched a great deal more and incorporates what might be referred to as a form of artificial intelligence. It literally has an ability to learn about a user's emails and decide whether it is good or bad. This is in addition to its original system employed of a technology that used "rules" to ascertain the good from the bad. This program is impressive-very powerful and keeps getting better with each new version. The developers of SA have done a wonderful job on this program and it is making a very big dent in the war against SPAM.

FIGHTING BACK
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The only feature missing in SpamAssassin is the ability to reject/delete SPAM. At this time it only TAGs emails as SPAM which gives the end email user to create filters within their email programs to separate and redirect the bad stuff into a special SPAM folder for review and deletion later. By creating filter "rules" on your email program, it keeps the SPAM from being mixed in with the good stuff in your email InBox and can tend to the bad stuff when you have time. On my own email programs, I have SPAM directed straight into the "Delete" mailbox and never look at it.

So now, thanks to SpamAssassin, we now have the ability to identify and "tag" SPAM emails with 99% or better accuracy. But, since the emails are only tagged, the emails still must be downloaded. Then the emails still need to be managed by the user and removed from the system, which takes a lot of time without regard to the annoying and offensive words we see in the Subject headers.

STILL TOO MUCH WASTE
Needless to say, most of our users have asked if there is some way to delete the SPAM right at the server so they didn't have to sit and twiddle their thumbs waiting for several megabytes of unwanted SPAM to download, just to get the good emails. This is especially bad for those who must pay by the minute or hour for the Internet connection, plus have slow 28kb or 56kb connections. Any such waste of time and bandwidth is a bad thing and so, SPAM is not without considerable cost to both the mail server and the end users.

In our own case here, we were reluctant to blindly delete our users' emails for concerns about losing the occasional good email. However, the complaints continued to grow and so did the request for elimination of SPAM at the server level. Being on both sides of the servers as an administrator and as a user, I fully understood and could appreciate the users' reasons for wanting the deletions, even at the risk of losing an occasional good email. Plus, we had been using SpamAssassin for several months and felt very confident about its abilities. In fact, in keeping an eye on my own emails, I had never observed the mislabeling of a single important email. Notice I said "important."

After a great deal of study and research into a sound method to employ, I found a way to do it. Relying upon SpamAssassin to identify the good from the bad emails, it was then a matter of how to program the Unix mail system into separating the emails, then delivering only the good ones to the users' email boxes and divert all of the SPAMs into "vaporland." Furthermore, my design of this system allowed this system to be applied to users' according to their choice. Thus, they can elect to have the bad stuff deleted at the server or leave it the way it was and deal the SPAM themselves.

NO MORE SPAM!
Since invoking the above new system that separates and deletes the SPAM, it's an amazing relief from the distraction it was causing. The amount of annoyance, effort and distraction wasn't so obvious until such an abrupt change. This warm feeling of relief is probably because the SPAM load has grown in volume over a period of years, but it suddenly disappeared in an abrupt manner showing an immediate contrast. The users are happily stunned as well by the same reaction.

Alas, although they have the same abilities available to them, the ISPs out there are not as likely to adopt the delete method as we did here because they have thousands of users, or millions for the larger ones. In their case they have more exposure to loss of good emails and complaints. If they do use anti-spam programs, even their spam-filtering program thresholds are commonly set very high and consequently allow much more bad stuff to escape tagging as SPAM. Some are not filtering and tagging at all, so their customers receive everything without the slightest hint which emails may be bad stuff.

WOULD YOU LIKE NO SPAM TOO?
As a result of the current mixed state of spam-fighting where some have some level of filtering, some with none and most if not all require users to download like we used to here, it occurred to me that perhaps we could provide the service as an alternative. It would be very simple to set up so that our servers could eliminate your SPAM just as described above.

We have several dedicated mail servers here, so capacity is not a problem and the system could be set up to handle your emails within a few minutes. If interested in eliminating as much as 99% or more of your SPAM and saving time and money, just email us at: deletespam@antennex.com

Some Notes on LPDA Stubs
By: L.B. Cebik, W4RNL

Log Periodic Dipole Arrays (LPDAs) very often employ shorted transmission line stubs connected across the phase line at the rear-most element terminals. The function and operation of these stubs is not as well understood as one might hope. In this column, LB offers notes to clarify the situation somewhat.

LAB NOTES: The DSA or Dipole Simulation Antenna
By Joel C. Hungerford, KB1EGI

Last winter, Joel read a description of a dipole's operation that said the delay from the drive point to the end of the wire and back through the air put the E field and the H field in phase, allowing the dipole to radiate. The source also said that energy flow in an antenna was toward regions in space where the current and the E field were in the same direction. Joel suddenly thought, "That can be done with a link coupled tank circuit, like the output circuitry of an old tube transmitter, or an I.F. transformer in a receiver."

Antenna System Tuning
By Fred M. Griffee, N4FG

Fred says in much of his reading, experimenting, and discussions, it is often found that there is an absence of recognition of the conjugate impedance match which he thinks can be somewhat true, depending on the antenna system aspect. Another area of his discussion addresses the use of high or low pass filter matching network design when used as an antenna tuner.

The GAP Super C Analyzed: Part 2
By Claudio Re ~ I1RFQ

In last month's Part 1 of Claudio's review, he delved into the theory of such a design and provides computer simulations showing the bandwidth, gain, patterns, etc. of the signal produced and how it is believed produced. This month in Part 2, Claudio takes the device to the test range for other important parts of the review-field-strength tests in a "clinical fashion." The article provides these "reality checks" to compare the results against the claims of the company, and to verify if it is really the device doing all of the work, or the feedline or surroundings that may enhance the signal--or all of the above.

The Crippled Loop
An Electrically Steerable HF Antenna
For Limited Space Installations
By William C. Miller, KT4YE

Many radio amateurs are unable to erect external antennas and are forced to find alternate locations. A prime candidate is often the attic. Unfortunately, attic antennas suffer from many shortcomings. If vertical, they are usually inefficient, due to the lack of height. If horizontal, they usually meander around, leading to inefficiency and undefined radiation patterns. Occasionally, Hams have installed beams in the attic, but these antennas are essentially impossible to rotate! Bill says, the “Crippled Loop” addresses most of these issues. It has significant gain over a dipole, is broadband, and offers substantial front-to-back ratio. Best of all, it can be electrically “steered” through 360 degrees using readily available parts and techniques.

The Low-Down NVIS Beam
By Dave Cuthbert, WX7G

If you like to work close-in skywave propagation then this antenna might be just the thing for you! And best of all, it doesn’t need to be high in the air. In fact, the 40-meter Low-down NVIS Beam hides nicely in a Closed Community and Restricted neighborhood.

Well, there you have it, folks—thanks for listening and remember, the reading lamp is always on for you in the reading rooms. If I can be of further help, I'm just a Stone's Throw! away. July 2003 antenneX Online Issue #75
reGARDS, Jack L. Stone, Publisher jack@antennex.com