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Spam Filtering: Why Does It Happen?

Rachel Gianfredi Archive

We often receive emails from customers who claim they received high bounce rate reports from their Email Service Provider (ESP), even after validating the email addresses on their lists with our service. This often occurs with customers who have not mailed to a specific list in a long time, or are new to an ESP. These customers will see messages from their ESP similar to "554 Reject by behavior spam" or "554 Spam violation.While it may seem like certain email addresses are labeled with these messages because they are invalid email addresses, that is actually not the case.

These messages are a result of Spam Filtering. After sending your message to your desired recipients, even though they may be opt-in contacts, you may still be marked as spam.  There are many reasons this might happen and we're featuring two of those reasons below.  In next week's follow-up post, we will have additional resources and information for you.

  • Content scanners have recognized something fishy with your email. Content scanners run through your messages to see if there are indicators of a typical spam message.
    • Text formatted in ALL CAPS 
    • Too many images
    • Your code is messy
    • Illegal characters in your content
  • Your recipients have marked your message as spam.
    • The content they received is not relevant for what they opted into
    • Your content is inappropriate
    • You are mailing to an address that did not opt-in to your mailings

It's important to note that the reasons for these messages are not related to whether or not the email addresses you're sending to are valid. If we've validated a list of emails for you, and you mail to the correctly identified "verified" group, then it's very likely that your bounce rate does not correspond to the validity of the emails on your list, but rather the content of your message.

Spam filtering is a complex topic, so if you need hands-on help, we recommend retaining a deliverability consultant or using many of the available online resources. We are good friends with many industry folks, so if you'd like to reach out to an organization in particular, we're happy to introduce you to a specific contact there!

MailChimp has a variety of helpful resources for this, and should be able to point you in the right direction. Other good resources, if you want to go the self-taught route (which is certainly doable!) are articles from Return PathWord to the Wise, and Spamhaus.  All of that being said, here are some of the many possibilities your message is being filtered as spam:

  1. People are reporting your message as spam.
  2. People are not engaging (opening, clicking links) with your message.
  3. Spammy keywords. For example, “wealth”, “$”, “affiliate”, “revenue”. These all have legitimate uses, of course, but tools like SpamAssassin use them as part of their scores. There are websites out there where you can send them an email and they’ll give you a SpamAssassin report that you can use for better insight. Your ESP might have similar tools, as well.
  4. Poor IP reputation from other campaigns. Your sender reputation lasts for quite some time, so if you've harmed it through practices of an earlier campaign, later ones will also feel the damage (Think of it like a credit score!  One late payment can cause your score to plummet.)
  5. Poor domain reputation. This could mean your sending domain, your tracking domains, your landing-page domains, etc.
  6. IPs/domains that are new to email marketing and you don’t have enough reputation yet so receivers aren’t taking a chance.

Other resources that could help you with email marketing best practices (and where we have many contacts!) are the Email Experience Council and Inbox Group.