Spam Filters

How Spam Filters Operate

Spam filters look at a long list of criteria to decide whether or not your email is junk/spam. The list of content that is considered spam criteria is constantly being adapted. Spam filters learn more about what junk content looks like every time someone clicks ”this is junk/report as spam”. Some spam filters even sync with each other to share what they’ve discovered. There is no universal formula, but there are a few guidelines to help you avoid common design mistakes that often send email marketing directly to junk folders.

The Spam Filtering Process

When you send an email campaign to your subscribers, your messages have to get through their ISP’s spam filters, then their email application’s spam filters. It's surprisingly easy for an innocent and legitimate email to be mistaken as spam (this occurrence is called a "false-positive"). It therefore helps a great deal to understand how a spam filter works. The following is a brief overview of what to look out for when sending your campaign to your subscriber list.

The Subject Line

The spam filter is not the only hurdle you’ll encounter, your subject line is how your recipients will judge whether or not to open or delete your message, and so it HAS to be relevant. Try to make your subject line concise so the recipient knows: who sent it, and what it refers to. Make it intriguing, but relevant to your readers. Also it should assure them of where the message came from, and what it contains. For instance, if we sent a Total Send newsletter with the subject line, "FREE GUIDE INSIDE! INCREASE OPEN RATES NOW!!!!!" we'd be making a huge mistake. Something like, "Your guide to improving open rates" would be much better. Avoid spam words and phrases, like FREE, act now, limited time, insurance, casino, coupons, click now, open immediately, etc. Also avoid using expletives and redundant phrases. Don't try to be creative with numbers/symbols in place of letters, like: V1AGRA, @CT N0W, CH01CE, etc.

Who is the message is addressed "To:"

Checking your mail seems very impersonal when you receive a letter that is addressed to, "CURRENT RESIDENT" or "TO WHOM IT MAY CONCERN". It's obvious that it was generated by a computer.  Likewise, don't just address your email newsletter to the email address. Merge your subscribers’ first and last names into the “to:” field using Total Send’s personalisation links.

The content of message

Spam filters look for "spam triggers" both on “the surface”, and in the code of your email's content: Don't just send a single large graphic. This is considered spammer behaviour. Your HTML email needs a good balance of graphics and text. If you're sending a simple piece to your recipients, and all it takes is one image to get your message across, you can still include some text at the bottom of your newsletter, such as an "unsubscribe" link, and your physical mailing address, company disclaimer etc. Always include a plain-text alternative with your HTML email. Spammers aren’t interested in doing so. It may seem like a lot of extra effort to write both versions of your email, but it is an imperative step. Also don’t make the plain-text version too bare. Spam filters compare your plain-text alternative to your HTML email. It’s considered “spammy” if 90% of the message is in HTML, and 10% is in plain-text. Spam filters punish lazy email marketers. A powerful and easy to use tool to do this is Premailer, which can be found at this link: Code your HTML email the right way. If your HTML email is coded badly, you'll look like a spammer. Broken images, missing tags, and non-web-safe colours are some of the things they look for. Never use Microsoft Word to generate your code! Word creates horrific HTML code and it’s almost a guarantee to work against you. Learn how to code HTML properly. Or pay someone to do it for you. It is worth the investment of time or money.

Avoid these common mistakes:

•     Using spam-like phrases such as “Click here!” or “Once in a lifetime opportunity!”

•     Using! Lots! Of!  Exclamation marks!!!!!!


•     Colouring fonts bright RED or GREEN

•     Coding sloppy HTML, usually from converting a Word file to HTML, or using Publisher.

•     Creating an HTML email that contains nothing but one large image, with little or no text (spam filters can’t read images, so they assume you’re a spammer that’s trying to trick them).

•     Using “Test” in the subject line

•     Sending a test campaign to many recipients within the same company (that company’s  email firewall assumes it’s a spam attack)

•     Designing HTML email in Microsoft Word and exporting the code to HTML (That is coded badly, and spam filters hate it.)

The Sender's Email Address

Some spam filters require that the sender of their mail must be "white-listed" or they are viewed as a stranger. And with being labelled a stranger, the spam filter will automatically categorise your email as spam/junk, or it will become unreasonably strict when judging your email's content. When people subscribe to your newsletter, it’s a good idea to ask them to "add this email address to your contacts list, to ensure proper delivery." Placing this request on your subscription confirmation screen, and all welcome emails will help in the battle against the spam filters. Some people place this at the top of almost every newsletter they send. When sending your mail and deciding your “sender” information, it’s best if you're not using anonymous details, like a free email account (Yahoo, Hotmail, etc.). Having a public email domain on your reply-to address will knock your spam score up further. For the best results - setup a real email address with your company’s domain name. Then get your users to whitelist it. Also, never change it. This ensures it will remain widely whitelisted and will prevent the need to whitelist another one.

The Domain Name

Some spam filters check to make sure that an email claiming to be originating from a particular domain name did in fact originate from that domain name. This is called "authentication" it's slowly becoming a normal procedure. Emails that are not "authenticated" are either classified as "junk/spam" or are flagged as "suspicious."

Community-based reporting

Whenever an email recipient clicks the "this is junk" button for a particular message they received, that "complaint" is sent to the ISP. If enough of the ISP’s users report an email from you as spam, then the ISP may block all your future email to their servers.

Do not let Spam Filters deflate your efforts

Most of the trusted spam filters out there aren't "black or white" with their algorithms. They're usually quite "realistic" about emails, and they use a well-rounded combination of criteria. SpamAssassin is an excellent example that you can learn from. It assigns "severity points" for each "rule" broken by messages. For example, using "CLICK HERE!" you could get 0.5 points added (for each occurrence in the message), while using bright red fonts might get you 0.1 points added, and including the word, "V1AGRA" in the subject line might get you 4.0 points added. It will count up the total score, and if it exceeds a certain amount (which is set by the person who installed it on the server), the email is labelled as "spam." When you write your email newsletter, don’t be paranoid about using phrases like "Click here" a few times in your newsletter. As long as the rest of your newsletter checks  out, and you don't break too many of the rules mentioned above, spam filters will let your emails through.