by Anna Wybieralska Sep 15, 2015

Get acquainted with spam filtering.

Many systems, including Elastic Email, use a spam filtering system referred to as "Spam Assassin", or less commonly "Apache Spam Assassin". It can be confusing to try and understand what exactly Spam Assassin tests for, why they are testing for it and how to fix your legitimate email so it doesn't get filtered as spam. This is our brief guide on the most important things to understand regarding Spam Assassin.

What is it? And where did it come from?

Spam Assassin is a computer program which filters and tests email in order to determine, (or try to determine) whether or not it is considered spam. It is considered an 'open-source software' which is built by contributing developers on a volunteer basis. It's most basic building blocks were in place starting in 1997, but eventually, in 2004 it became a project headed by the Apache Software Foundation and then the program was officially renamed Apache Spam Assassin sometime after 2004.

Why does Elastic Email use this to test email?

Elastic Email uses Spam Assassin as a tool for our customers - not a punishment!  Millions of email servers use Spam Assassin to check email. When you send mail out through Elastic Email it is going to be received by servers. These servers also use spam filtering tools (Spam Assassin!)  that are going to look at your mail and decide whether it gets to go through to the intended recipient. If your mail looks like spam (even if it's not spam) it isn't going to get to your subscriber. So, Elastic Email wants to help you solve any problems with your mail ahead of time so it has a better chance of successful delivery. The Spam Check Results on your account can seem harsh sometimes, but it's important to treat them like a guide - those results are there to give you a 'heads-up' about how your mail might be seen by recipient servers. The spam filter results are not necessarily trying to tell you your mail is spam, only that your mail might look like spam.  You can find this information in your Elastic Email account by clicking on the following in order: Account >> Reputation Details >> Content Analysis

What tests do they do? When is email considered spam?

Apache Spam Assassin uses sophisticated algorithms, including Bayesian spam filtering and does hundreds of tests on mail. You can take a look at the entire list here. When an email is filtered through these tests, a score is compiled that determines the likelihood that the email is spam or not based on whether that email is testing positive for certain criteria. Simply put, the higher the score, the more likely the mail is spam (or will be filtered as spam, even if it's not).

What do the tests mean? How do I fix my email?

The tests are somewhat cryptic for sure. For instance, you've probably seen something that looks like this:

RAZOR2_CF_RANGE_E4_51_100 or maybe this: URI_OBFU_WWW

What? You will see a short explanation in addition to your score in your spam results that will help you understand how to correct or change your mail. We will take a closer look at the two examples above however to give you an idea:


The description of this test from Spam Assassin is this: "Razor2 gives confidence level above 50%"  - but if you take it step further, you find out that it is referring to another spam filtering network called Vipul's Razor. Through collaborative user contribution, Vipul's Razor is an ever-changing consensus-based system that then assigns confidence values that suggest the likelihood that a given email is spam - in this case, there is a 'between 50% and 100%' chance that the mail is spam.

Now, this case is tricky because it is not a specific rule that you have broken, (like accidentally adding "click here" or "dear friend" to your mail - spam filters don't like those either) but your mail has basically been compared to other mail that turned out to be spam and so now Vipul's Razor thinks your mail might be spam too! How do you solve that? Well, first you look at other things that might be listed as problems with your mail and fix them if they are simple - for example if you see this:

DEAR_FRIEND ( Described by Spam Assassin as "Dear Friend? That's not very dear!")

... then you know you need to remove that text from your email template to help lower your spam score. Then, the next step is to try changing your email format, use a good ratio of text to images (one large image won't do well) and consider changing your sending domain if none of your format changes work. One thing to know about Spam Assassin is that if your mail 'fails' one test,  is likely not enough to consider it spam. 

The second example is this:

URI_OBFU_WWW   - described by Spam Assassin as "Obfuscated URI"

An obfuscated url or URL is a website address that has been concealed or is misleading. This can mean that a user has added a link to a website using inviting text such as "Click here to get this deal" but instead of going to the expected website, the user is re-directed or ends up on a spoof or fake website that is imitating a legitimate one. This method is often employed by spammers and in phishing attacks.

See this HTML as an example:


When you use something like this, the displayed text in your email matches the actual URL. There is no deception and your mail will have a better chance of not being seen as spammy.

Not as good: Click here!

In this example, your mail might be seen as misleading because the text you click then takes you somewhere else. Try to avoid this.

If you're seeing this in your spam check results, check your links and you need to make sure you haven't made any spelling mistakes for your domain setup. Then, you need to ensure that you aren't misleading your subscribers - your mail must not be unsolicited and needs to comply with Elastic Email policies.

What if I can't make a change they think I should?

Spam Assassin and other spam filters are a continuous work in progress, and because they are based on percentages, probabilities, interpretation and other tests, they can make mistakes. So, if you find that Spam Assassin has given a score to your mail which isn't accurate (you checked carefully!) then don't stress too much, make the changes you can and remember that a single test fails won't necessarily mean that your mail goes to spam - there are a lot of factors that influence where your mail ends up - engagement levels are a big one for instance.

Where do I find out more information?

Many people are always looking for more information about this subject and simple Google search can yield helpful results if you're not sure what your Spam Check Results mean.

And, do we really need spam filters?

Yes! They are a tool to help protect legitimate mail senders from being lost in a sea of bad email. Even if it's frustrating to spend time interpreting spam filter meanings, it really is in your best interest to take advantage of this tool. Elastic Email support staff is also here to help you 24/7 if need some extra help figuring it all out. You can contact us anytime here.

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Anna Wybieralska

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