Spam Filters: What you need to know!
By Dori Friend

As an active email marketer, correctly directing your email campaigns has never been more critical. As you are well aware, actively managing your bounces or avoiding spam filters completely is ideal. You want to ensure that the greatest number of intended recipients actually get reached with the message that they asked for!

Recently, it has been reported that Yahoo! blocks as much as 22% of email, AT&T blocks 12% and AOL, with some 30 million subscribers, blocks 18%. Marketers themselves estimate that as much as 15% of their legitimate e-mail communication (emails for which recipients have opted-in) is getting labeled as spam.

Think about it – if you sent 100,000 pieces of direct mail through the post office and 15,000 of them got thrown away by the mail carriers would you be happy? Consumers, on the other hand report that roughly one-third of desired email is not getting through to them, because it is being blocked by spam filters.

To be sure, the filters themselves are not perfect and often times they err on being "over protective." A good number of them have even become quite aggressive as of late, and the number of spam filtering options is growing as well. As many as 150 companies now offer spam filtering products.

The spam filter technology is getting "smarter" too. For example, some servers (known as challenge systems) send e-mail back to the original sender and require a reply before they forward the email onto the account holder.

The idea here is that a machine cannot reply to a request for specific information, so if the email is genuine it will be answered and then forwarded. America Online recently announced a new spam filter that can actually "learn" the preferences of each of their subscribers. This will be an interesting technology to watch.

The filtering itself can be broken down into three groups: Content based filtering, Volume based filtering and Blacklist filtering.

Content-based filters block email messages that appear to be spam because they contain words, symbols and other indicators that identify the email as potential spam. These are where "triggers" come into play.
Volume-based filters are used to counter the high-volume demand from large junk mailers.

For instance, if email messages exceed a certain pre-determined limit, like messages sent per second , the email messages may be blocked or redirected to a junk mail folder.

Blacklists are lists of IP addresses that are associated with known and alleged spammers. Reportedly, there are close to 300 spam blacklists in use today by ISPs and system administrators (ouch)!

The Internet spam filters work by reviewing incoming email and "checking" the file for certain factors. Depending on what these filters find or don’t find, points are added to or taken away from a scoring system.

These filters (you may be familiar with such names as SpamAssassin, Bogofilter, and SpamProbe) look for certain patterns in your email, and assigns "spam points" depending on certain words, phrases, or even colors!

If your score is 5.0 or higher, your email subject line may be edited and "* SPAM*" appears at the start of your email, or your email is redirected to a "bulk" type of mailbox (how RUDE)! The key point to remember about the numbers is this: the lesser the score the better (kind of like golf)!

If we were to categorize the two primary areas where spam filters err, they would be in the areas of "false negatives" and "false positives." A false negative is when an email that is indeed spam gets through the filter, and a false positive is when a legitimate email gets caught in the filtering system.

So, what can you, as a legitimate e-mail marketer do to ensure that your messages reach the intended recipients?

Many marketers are doing a combination of things to combat this aggressive filtering. One way is to "tailor" their messages so as to stay away from filter "triggers".

You can also go it alone, and try to avoid the spam filters, but beware, trying to outsmart the email filters is a daunting challenge There do exist some words that are generally believed to be "triggers".


The best thing is to do with regard to staying away from triggers is to frame your messages so that they have the best chance of getting through these filters. Make sure that your clients confirm the fact that they have "opted-in".

Send them a confirmation e-mail to the address they specified and ask them to reply that they indeed want to receive mail from you. Once this is done, be sure to ask them to add your e-mail to their address book.

I bet that the recent "DO NOT CALL" list could easily be morphed into a "DO NOT EMAIL" nationwide list. If it does, you already have your proof with your confirmed list that your clients want to hear from you!

Another good option that is gaining ground is a called the Habeas warrant mark. This requires a license to be purchased, but it is kind of like the "Good Housekeeping Seal Of Approval" for e-mail marketers.

Habeas is forming partnerships with emailers and spam filters to establish credibility and to verify opt-in emails. SpamAssassin, for example subtracts 4 points from your score if Habeas appears in the header of your email.
Spam filters are also on the lookout for emails that contain a lot of HTML and they pay close attention to the links that are in your content.

For example, if SpamAssasin "reads" that your email contains more than 50% HTML, you get socked as many as 1.78 points. Filters are also picky in regard to hyperlinks. Want to get a quick3 points added to your score? Just have a link with the IP numbers and not the domain name.

The ability to unsubscribe is also a target of spam filters. It is best to avoid using lines such as "Click here to unscubscribe" and "Use this link to". Apparently, this is a tactic that many genuine junk-emailers use to give the appearance of their messages being legitimate.

The best way to do this is to this is to ask that your respondents send a separate e-mail to a separate address asking them to be removed from a list.

As for the larger Internet Service Providers, (for example, MSN, Earthlink, YAHOO!, Hotmail, and AOL), they seem to have their own personalities when it comes to Spam Filters. Some would be considered more of strict "gatekeeper" than others would.

MSN, in their policy, states specifically that, you (the sender or the receiver) may not use or contain invalid or forged headers or use or contain invalid or non-existent domain names. They go on to say that "if Microsoft believes that unauthorized or improper use is being made of any MSN Service, it may, without notice, take such action as it, in its sole discretion, deems appropriate, including blocking messages from a particular Internet domain, mail server or IP address." So basically, if MSN doesn’t like it – it doesn’t get through.

The Earthlink filter system has been dubbed as "too much of a challenge" by some. This ISP uses what is known as a "Challenge-Response" system. The filter device requires senders to prove they are human rather than an automated program. When a recipient gets e-mail from an unknown sender, Earthlink software automatically returns a message -- a challenge -- requiring the sender to perform a task such as filling out a form. The idea here is that a "blast" program cannot answer the challenge, so it must be spam!

Yahoo and Hotmail make use of a system by Nullifier Pro, which claims to block 99% of unwanted junk e-mail with zero false positives (yeah right)! Each incoming E-mail is analyzed for semantic identifiers of words and phrases based on the message, its attachment, subject and header.
It features automatic spam definition library, foreign spam blocking, and friends list and advanced abuse reporting, but most of the time it just ends up in a "bulk" type folder.

AOL recently added new spam filters that are being advertised as able to "grow" with each user’s preference. This particular filter "grows" or learns" by the AOL subscribers reporting spam to AOL, which then "pools" these into one big database for their online community as a whole and for the individual member individually. When AOL talks, people listen because of the large subscriber base, so this one will be one to watch. Only time will tell if this is "truth" or "advertising."

It is really still the dawn of Internet marketing. Congress may in the future pass some kind of e-mail "fees" – expect the post office to push for something like a use tax or "stamp price" for e-mails as they are loosing billions in revenue in mail that is not sent through their system.

It is still hard to beat the cost to benefit ratio of email marketing. The response rate does not have to be all that high for the mailing to be considered profitable since it really costs little more to send 20,000 emails as opposed to 100 emails.

Therefore, email marketing is and will continue to be a tremendous "bang for your buck", and a wonderful tool of choice for the professional marketer.

© Sonic-Rocket Marketing, 2003