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How to avoid spam filters and increase email deliverability

How to avoid spam filters cover

Email marketers spend a lot of time crafting email campaigns. From testing various email copy to crafting enticing subject lines in an attempt to maximize open rates and click through rates. But if your emails end up in peoples spam box instead of their inbox, your emails simply won’t get read.

A recent IBM study highlighted the impact deliver ability rates can have on your email marketing. Their study found that 17% of emails never see the inside of the recipients inbox.

The only way to avoid spam filters is to understand how spam filters work and how you can avoid them. In this post we’ll go through the effects bad deliver ability can have on your campaigns, the different spam filters and how they work, and how to craft emails that will avoid spam filters.

Effect of bad deliver ability

In 2012 Sony launched an email marketing campaign to cross-sell the PlayStation Vita to existing PlayStation customers. The campaign was sent to 4.2 million people and resulted in 9,236 devices being sold, generating €2.9 million in revenue.

Lets say for arguments sake that 17% of the emails Sony sent out ended up in spam boxes. That’s 714,000 emails. Had all those emails been delivered, Sony could have potentially sold an extra 1919 units, generating an extra €602,537 in revenue. That being said, you’re not going to have 100% deliver ability. But there are tricks you can use to maximize your email deliver ability rate.

How spam filters work

To maximize deliver ability rates for your campaigns it is really important to have a basic knowledge of how spam filters actually work and on what basis they flag an email as spam.

Spam filters generally use a scoring framework and look at a few things when deciding what to do with emails: the sender’s technical specifics, the email’s content, reputation, and engagement.

Technical Specifics

Spam filters will typically check for appropriate email authentication and your sending IP’s reputation when deciding whether to deliver your emails or make them disappear into cyberspace.


Here we’re talking about the actual content that is in your subject line and body of the email. Spam filters work by scanning the entire copy of the email searching for specific words typically found in spammy emails. In addition to the copy of the email the filters will look at formatting, link types, and image-to-text ratio. Some services like gmail will also look at spammy text within an image using image recognition.

User Defined

This is also know as bayesian filtering and it’s one of the most widely used type of spam filters. These filters work by watching recipients classifying emails as junk. When a user classifies an email as spam the filter looks at the words and phrases in the subject line, email content, links, and so on. Over time, the filter learns to scan for those traits in every email.

Tactics for avoiding spam filters

Now you know how spam filters work, hers how you can avoid them and maximize your email deliver ability rate.

Avoid spam words

One of the fastest ways to end up in a subscriber’s spam folder is to load your email up with words that most email service providers have identified as common words in spam email. A good rule of thumb is, if it sounds like salesman lingo then it’s probably a spam trigger word.

Unfortunately there isn’t one simple list of a all the words you should avoid. This is because spam filters are so sophisticated and words will vary between industries.

Here’s some examples of spam words to avoid if you are in the financial or marketing space:


$$$ Affordable Bargin
Cash Cash bonus Cheap
F r e e Fast cash For just $XXX
Get out of debt No fees Save big money
Save up to Stock alert Subject to credit
Unsecured debt US dollars Why pay more


Click here Email marketing Form
Increase sales Increase traffic More internet traffic
Internet marketing Marketing solutions Month trial offer
Online marketing Visit our site Web traffic

For a more comprehensive lists of words you should avoid, check out this industry specific post by Hubspot.


Suspicious formatting not only triggers spam filters, it might also annoy your recipients into marking your emails as a spam. Here are some basic formatting tips when designing your emails:

  1. AVOID CAPITAL LETTERS – avoid using capital letters in your email copy and subject lines.
  2. Don’t over-use punctuation marks!!!!!? – try and avoid excessive use of punctuation marks, especially in a row.F
  3. Keep fonts consistent – avoid bright red fonts or going crazy with colors, styles, and formatting.
  4. Provide an unsubscribe link – This is the law. If your emails are missing an unsubscribe link they’ll trigger spam filters.
  5. Don’t link too much – try and include as few links as possible in your emails. For any links you do include, avoid using URL shorteners as they’re frequently abused by spammers.
  6. Make sure the HTML code is clean – sloppy HTML code can get you spam filtered. If you use a drag and drop editor to code your email sometimes they include useless code that’s invisible to the user. This makes filters think you’re a sloppy spammer.
  7. Include text – Sometimes it can be appealing to just use a bunch of slick graphics and images. But spam filters can’t read images so they assume you’re a spammer trying to trick them.
  8. Avoid mashing text with numbers – creative spelling is a classic sign of a spammer trying to include words they shouldn’t. For instance: Cl1ck h3r3 f0r fr33 cash.


Subscriber engagement is a huge part of getting emails into people’s inboxes. If your subscribers consistently ignore your emails, failing to open and click your emails, mail servers are going to presume you’re a spam sender. If your emails are getting low engagement they will end up in spam boxes, even if your subscribers aren’t marking the email as spam.

Here’s some basic things you can do to avoid being flagged as spam if your emails have low engagement rates:

  1. Have a policy for unengaged recipients – if someone is constantly ignoring your emails, remove them from your list. Keeping them on your list will do more harm than good.
  2. Keep email frequency low – if you’re bombarding your subscribers with emails over a short period of time you’re increasing the likelihood they will be unengaged.
  3. Keep your email list current and clean – if you start sending campaigns to old lists and prospects then you’re running the risk of the recipients marking your email as spam as they’ve probably forgotten who you are.
  4. Remove bounces – if an email bounces, remove that recipient from your list.


Email marketing continues to be one of the most effective channels. But if your emails aren’t ending up in people’s inboxes then your emails aren’t going to get read and you’ll miss out on all that potential revenue.

Now you have a basic understanding of how spam filters work and how you can avoid them you should keep these tips in mind when crafting your next campaign.

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