Having your emails canned by spam filters is an email marketer’s worst nightmare. You may put endless hours in designing the perfect campaign but ruin everything in the blink of an eye. One sloppily worded phrase or a broken HTML code can trigger a set of warnings and make the spam filters believe you are spamming the recipient.

Remember that you don’t have to be a spammer to be spam-filtered. Even the best white-hat marketers, who only send permission-based emails to their double opt-in lists sometimes get blocked by the often overzealous filters.

There is no quick-fix method you can employ, nor a proven recipe for success. Email marketing is learned by trial-and-error; nevertheless, if you want to have the best shot at delivering emails straight to the inbox, you need to understand how spam filters work.

What spam filters basically do is have a look at your message and match it against certain criteria and assign some points according to how much ‘junk’ your email contains. For example, mentioning Cialis, Perfect Rolex Replicas or some other keyword on top of today’s spammers’ lists would most likely result in your mail being flagged as spam immediately.  However, something more in the line of a mortgage or credit repair sales pitch will be analyzed more in-depth and, once the total point count goes above a certain threshold, your message will be flagged as spam.

SpamAssassin, one of the leading open source email spam filters on today’s market, shows its default list of phrases it looks for and the points it assigns. Here are some examples:

• Subject contains the name of a prescription drug (sometimes intentionally spelled wrong), like Viagra, Cialis or Valium – between 0.68 and 2.66 points
• Message headers are too long (no real company, ESP or ISP can afford sloppy email headers, so these have to be due to a careless programmer who wrote the spam piece of software) – 2.50 points
• Subject has lots of exclamation marks and/or question marks (‘WOW Have a Look At This!!!!!!!’) – depending on extra filters and checks, can be assessed with 0.20 to 0.91 spam points
• Invalid date in header, when matched against the recipient’s server’s date and time. A wrong EST timezone, together with other broken tests, can be scored with as much as 3.58 points.
• Various other HTML errors can receive up to one spam point (like text before the end BODY or HTML tag,
• Mentioning a product is ‘All Natural’ will get you a bit over 2.50 spam points, so pay attention to how you promote your holistic products. The same goes with offering a money-back guarantee or offering a free mobile product, be it cell phone, notebook or tablet.

With so many constraints, your next question will be on what minimum threshold you need to stay under. There is no general answer for that, since spam filters are configured differently on each server. The minimum value is most often solely the system administrators’ policy and depends on how fed up with spam they are—if they set a very low value, then only white-listed messages will pass through.

This wraps up the short insight on how email spam filters work. In a future article I will describe the common mistakes you should avoid and how you can deliver straight to the user’s mailbox.