Spam Filters and the Common Challenges they Pose
© 2003, Susan Sweeney / Connex Network Inc.

There is an ever increasing volume of spam. As a result there exists the need to find ways to control and eliminate it. The focus of this newsletter is on common spam filters and issues encountered by legitimate email marketers. Unfortunately, many legitimate emails become casualties of spam filters and this poses a huge problem for credible companies. When a legitimate email is blocked by a spam filter this is called a “False Positive.”

Spam filters cost legitimate businesses a lot of money. According to Assurance Systems it is not uncommon to find cases where 1 in 6 legitimate campaign emails are caught by spam filters – that is a HUGE loss when you consider this amounts in part to lost sales and revenue! On the same note Ferris Research estimates that the cost of spam in 2003, including computing resources and lost productivity, is $10 billion in just the United States.

Understanding the different types of spam filters and common triggers is the first step in the right direction to maximizing the delivery rate of your email campaigns. Spam filters exist at three different levels, though the end result is always the same; a message that never reaches its destination. Your message could end up in a spam folder, deleted, or passed to a blacklist as an accusation of being a spammer. The three layers of spam filters are:

  1. The Internet level – emails are filtered before reaching the ISP
  2. The ISP level – emails are filtered at the ISP level
  3. The end user level – emails are filtered by software applications in place on the end user’s PC

There are several methods that spam filters employ to catch spammers; however, to keep it simple we will just consider the common `point system.’ Once you build up X number of points you win (or lose as the case may be). Spam filters look for certain patterns and add points depending the number and severity of the occurrences.

If your total sum of points reaches a certain level your message is considered spam and your message is filtered. In some cases you might be doing something considered so wrong that it costs you all the marbles. For example, if you send to a huge volume of people at a specific ISP the ISP might decide that there is no way they are letting your messages through.

Tips & Techniques

Knowing your entry barriers and what to avoid can help you improve the successful delivery rate of your email marketing campaigns. Here are some of more common reasons behind legitimate messages being blocked.

Failure to get on whitelists poses a big problem - A whitelist consists of a list of e-mail addresses or domain names that are granted permission to pass a blocking program’s filters and deliver a message to the intended recipient. Most ISPs, such as AOL and MSN, have whitelists. Similarly, almost all individuals who use email have a white list – commonly referred to as their address book.

If you are not on an ISP’s whitelist and you try to send a series of messages to a number of their subscribers you can expect your message to be rejected from the get-go. Many companies are unaware or do not take the time to get whitelisted. It can be very time intensive as it requires taking the time to form a relationship with the ISP. Getting listed on a whitelist means having to prove you are legitimate and competent (e.g. good list hygiene).

Alternatively, you can use the services of a bonded sender who is already considered a legitimate sender. See the Bonded Sender Program for more details.

Assuming you are able to reach past the ISP or corporate gateway to the end recipient, you now face their filtering applications. Many users have filters in place to reduce spam. Likewise, many email applications have default settings imposed on the end user to filter out spam. If you are not on the end user’s safe list or address book your email will either be a) deleted, b) dumped to a junk mail folder, probably never to get read, or c) not display properly to the end user.

Another point to note here is that blocking filters can skew your ability to track open statistics by blocking stats tracking tools – this means your numbers will be off, but you won’t know by how much!

AOL 9.0 is receiving a lot of press, both good and bad, about its spam filtering technology. It is expected that over half of AOL’s subscriber base will be using AOL 9.0 before the year is out. The new AOL 9.0 is creating a lot of headaches for legitimate marketers. By default AOL 9.0 will block all images and links from a message unless the end user purposefully selects “Show Images & Enable Links” each time they receive a message from you or if the end user adds you to their address book.

What is your course of action? First of all, make sure the “message” in your email does not rely on images to get your point across. Ask them to add you to their address book! Tell them it will help ensure the messages they have requested will be displayed properly.

Make sure you send your email from the same email address each time or you have basically wasted your efforts in getting whitelisted. If your message happens to make it to the end user and he/she does not recognize the email address you’ve sent your email from because you are using a different account you could have a problem. The user might report your message as spam to their ISP or to an organization such as Spam Cop and then you run the risk of being blacklisted. Getting yourself off of a blacklist is a topic for another newsletter.

Using too many bad words will trigger spam filters! – There are many terms that people use on a daily basis and in their marketing materials that can trigger spam filters. The last thing you want to do is use a series of words or phrases that result in your email being blocked or dumped in a junk mail folder.

Just using one word or phrase is not likely to get your messages blocked, unless it is considered extremely bad. Phrases such as “reverse aging” and “compare rates” are two such phrases that rank high on the point scale. “Removes wrinkles” racks up over 4 points according to the SpamAssassin mail filter. Considering all it takes on average is 5 points to get filtered, a single phrases equating over 4 points is bad.

Trigger words can appear in the subject line of a message, in the body of the message, and in the “To:” email address field. Here is a small sample of common spam trigger words:

Filter Words in the Subject Line

  • Contains $$$
  • "100% free"
  • Contains word "ad"
  • apply now
  • Earn $
  • earn extra cash
  • eliminate debt
  • extra income
  • fast cash
  • financial freedom
  • free gift
  • free info
  • free offer
  • home based
  • online marketing

Filter Words in the Message Body

  • 1-800 1-888
  • 100% free
  • 100% guarantee
  • call toll free
  • debt free
  • earn extra income
  • email marketing
  • information you requested
  • joke of the day
  • life insurance quote
  • limited time offer
  • lose inches
  • lose weight
  • work from home
  • you have won

“To” Email Address Begins With

  • everyone
  • fellow marketer
  • free
  • friend
  • group
  • list
  • netmarketer
  • nobody
  • promotion
  • winner

This is just a very small sample! A good list of spam triggers can be viewed under the testing section of SpamAssassin’s Web site. This contains trigger words and common design elements, which is covered next.

What should you do? Minimize the use of words that are considered to be spam triggers. It is not necessary to stop using them altogether, but do not go overboard and be aware of how much weight they hold on the point scale!

Not considering the design and distribution of your email can cause trouble – Quite often it is the very design of the email that results in it being blocked. It goes without saying that if you are sending an HTML newsletter and the coding is incredibly sloppy the spam filters will be throwing up red flags all over the place. Take the time to make sure your code is clean.

Here are some common design and distribution issues that trigger spam filters:

  • Excessive use of punctuations!!!!!!!!!!!???!?!!
  • Sending attachments with your emails
  • The color blue in the HTML or links
  • Including a large number of hotlinks
  • Links not superseded by http://
  • Links that reference numeric IP addresses instead of a domain name
  • HTML-only emails (e.g. an email that is made up of all pictures and no text)
  • Emails that are too long
  • Sending your email to too many people at once who reside on the same ISP
  • Use of CC: or BCC: to a group of people
  • Sending email from your email browser (E.g. Outlook, Eudora) to a list of recipients
  • Stating in your mail piece that you conform to spam laws (As a legitimate email marketer, you shouldn’t have to say it.)

Even when you are trying to help your target market you can end up hurting yourself. As a matter of best practice (and in some cases law) you always want to give your target market the option to easily unsubscribe; however, using words like “unsubscribe”, “remove me”, and “click to remove” or similar claims are considered spam triggers in some cases. This development came about because so many spammers execute fraudulent unsubscribe options – to them it’s an ‘ah ha, it lives’ and then they know they can send emails to that account.

Lastly, an unhealthy list can get you in oodles of trouble. Email accounts that begin with postmaster@, abuse@, etc. are bad news if they are found in your list of subscribers. Remove them immediately.

We are all going to end up guilty of some of these. In fact, they likely help get your point across and improve the impact of your newsletter. By knowing common triggers you are in a better position have your mail delivered to its destination by being able to prepare your emails with spam triggers in mind. Remember, always be courteous and abide by industry best practices.

The best recommendation is to Test, test, test!

You can get a good idea of what works and what does not by getting Yahoo!, Hotmail, and AOL accounts and test sending your newsletter or emails to those accounts. Also, test your emails in popular email browsers such as Outlook and Eudora. Play around with their spam filter settings and see how that affects the deliverability of your messages.

Run your messages through spam checkers to evaluate your messages. You can use the results to refine your message. A selection of spam checker tools is included in the Tools & Resources section below.

This knowledge will help you with your daily email communication with customers as well. Spam triggers apply to your every day emails! You do not want a customer wondering why you never replied to their email when you really did and they just did not receive it. Also, abiding by good email etiquette and best practices you protect yourself from a legal standpoint.

Tools & Resources 

Check out the following Web sites that feature solutions and resourceful information.

Spam Checkers:

Many email marketing solutions include spam checkers already that will review your message and return a grade along with the reasoning behind it.

Spam Filters – Desktop and Enterprise:

Email and Spam Resource Sites: