How Spam Filters Work

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Protecting yourself against the legal implication of a violation of the CANN-SPAM Act is only the first battle in the email marketing war.  Once you understand spam laws, your next challege is getting your email message past the content filters used by internet service providers (“ISPs”) and into your client’s inbox.

To do this, it’s key to understand how spam filters work.  Spam filters look at some predetermined criteria to decide if your email is junk.  They score that criteria and if you’re message reaches a high enough number on the score, your email is relegated to a “bulk”, “junk” or “spam” folder.

One of the most popular spam protection companies, Spam Assassin, publishes the tests they perform on emails and the corresponding scores.  Here are a few examples:

  • Subject starts with a dollar amount (.600 points)
  • Subject talks about losing pounds (1.927 points)
  • Similar addresses in recipient list (2.499 points)
  • Message begins “Dear Friend” (2.683 points)
  • Message talks about how to be removed from mailings (2.907 points)

You can see how frustrating writing emails can be when one of the requirements of the CANN-SPAM Act, making sure there’s a clear communication of how the recipient can remove themselves from mailings, also penalizes you.

Further complicating the matter is that every ISP has their own list of criteria, and own calculation of the threshold that condemns your mail.

Crafting a filter-friendly email can be easy if you follow a few simple rules:

  1. Read Spam Assassin’s list of tests and avoid phrases they consider spammy, such as “free”. “act now” and “millions of dollars”
  2. don’t get cute with numbers or symbols that look like letters (ie V1agr@)
  3. avoid excessive punctuation or blank lines in the email
  4. using all CAPS (especially in the subject line)
  5. creating an html email that’s nothing but an image
  6. writing an html email first in Word then exporting as html (this creates slopping html code that spam filters penalize)
  7. Check against a filter test service.  Many free ones can be found online, as well as quite a few premium options.
  8. Get your clients to add your email address to their address book.  If you look like a friend to the filters, you have a better chance of getting to the inbox.

It should be noted that the criteria used by ISP filters is a dynamic list, constantly growing and adapting based on what is currently being reported as spam by users.

So every time someone reads your email and clicks on the Spam button, all the details of that message are added to their spam filter database.  Get enough clicks and suddenly your email address, ip address, domain name or product name is blocked by the filters.

The solution? Create a great relationship with your clients that leaves them looking forward to not only reading but also saving your emails, ensure that they are less likely to ever see a message from you and click their spam button.


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