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Avoid the spam filter: How to improve your email deliverability

By |Last Updated: December 10, 2020|9 min read|

Did you know? 51 percent of people discover new websites through email.

Email is critical for driving higher click-through rates to your website — and that increase in high-quality traffic can, in turn, do wonders for your SEO.

But to see the highest possible ROI, your emails need to reach your subscribers’ inboxes first. And according to a study by ReturnPath, 21 percent of legitimate marketing emails don’t make it past the junk mail filter.

Thanks to spam filters and legal intervention, even the most seasoned marketers are hard pressed today to avoid delivery issues.

So what can you do to increase your rate of email deliverability?

Spam and the law

In simple terms, spam is defined as an unsolicited email, sent in bulk, and typically for commercial purposes.

Spam is not only annoying, but also potentially harmful: Many spam emails are a ploy to obtain a consumer’s financial or personal information, which can then be exploited for credit card fraud, identity theft, or other such crimes.

Accordingly, various governments across the world have taken legislative action to help protect consumer rights. Let’s take a look at a couple of the best-known examples.

CAN-SPAM Act of 2003

The U.S. government has passed the CAN-SPAM Act of 2003, which established legal requirements for all commercial emails — not just bulk email.

Some of its basic requirements include:

  1. Clearly identify the person or organization sending the email.
  2. Use accurate subject lines.
  3. Offer an option to unsubscribe.
  4. Provide your business’s physical mailing address.

Today, most people consider CAN-SPAM to be relatively ineffective at stopping spam. That said, the law is still in effect, and violating it can cost your business up to $41,484 for each separate email. That will add up quickly… so don’t do it!


The General Data Protection Regulation (GDPR) is an European Union law that regulates how businesses must protect individuals’ privacy. It applies to any business that’s either based in the EU, or sells goods and services to EU customers.

The full scope of GDPR is pretty extensive, and you can read a more complete summary here. But in a nutshell, GDPR-compliant businesses must (among other things) secure “clear, affirmative” consent from their customers before using their information for commercial purposes.

Non-compliance with GDPR can cost your business a pretty penny: The maximum fine is 20 million euros or four percent of worldwide turnover, whichever is greater.

GDPR should help reduce spam, at least in theory, because EU residents will now only receive emails they’ve signed up for.

(In practice, GDPR actually hasn’t had a noticeable effect on spam levels so far, but for pretty technical reasons.)


The Canadian Anti-Spam Law, which has been in play since July 1, 2014, applies to anyone who’s either based in Canada or does business with Canadian residents.

CASL regulations apply to “commercial electronic messages” — which means any electronic message (like text messages, emails, and some social media communications), sent to an electronic address, that asks its recipients to engage in commercial activity.

Under CASL, you can send messages to people who have given express consent, orally or in writing, only after you’ve clearly laid out the following:

  • A clear description of why you need their consent
  • A description of the messages you plan to send
  • Your name and contact information — including your physical mailing address, phone number, email address, and website URL
  • An option to unsubscribe at any time

Failure to comply could result in fines of $1-10 million per violation. Such a stiff penalty could easily drive a smaller business into bankruptcy… which should be as good an incentive as any to stay compliant with CASL!

What makes a server reject emails?

Legislative efforts aside, email service providers themselves have good business reasons to ensure their users receive as little spam as possible: If someone’s getting too much junk mail, they’ll eventually switch providers.

Enter spam filters.

Spam filters use a set of predefined criteria to “score” how spammy an email is. If an email’s score exceeds a certain number, it’ll get rerouted to the junk folder.

The criteria used varies by ESP — and quite understandably, ESPs don’t make theirs public, as spammers could use that knowledge to bypass the filters.

Still, here are some common factors at play:

  • Email authentication: Is the email coming from a legitimate source?
  • The sender’s IP address: Has somebody with that IP sent spam mail in the past?
  • Campaign metadata: Who’s sending the email, and more importantly, are they acquainted with the person receiving the email?
  • Coding and formatting: Does the email contain sloppy code (like extra tags), link shorteners, rich media, or forms?
  • Image-to-text ratio: Does the email contain too many images, or overly large images?

How to improve email deliverability — 3 areas to note

Our tips for avoiding death by spam filter fall into three broad categories:

1. Technical safeguards

Take steps to authenticate your emails. Whether you’re using a standalone email marketing platform (such as Mailchimp or Constant Contact) or an all-in-one marketing suite such as HubSpot, the following three methods can help incoming email servers confirm that you are who you say you are:

  • Sender Policy Framework (SPF): Matches an email sender’s IP address against a list of IPs authorized to send emails via that domain.
  • DomainKeys Identified Mail (DKIM): Checks an encrypted “key” embedded in an email against public records to verify the identity of the sender.
  • Domain-Based Message Authentication Reporting and Conformance (DMARC): Requires an email to pass both SPF and DKIM standards before it can be sent.

Most email marketing platforms offer step-by-step guides for implementing one or all of these safeguards for your account — check your provider’s support resources to get started.

2. List management

Many spam filters use low email engagement rates — including low open rates, unsubscribes, and hard bounces — as an indicator of spam.

To avoid that, it’s important to get the appropriate permissions:

  • Don’t make assumptions. Even if someone is already your customer, don’t assume you have permission to email them!
    • The industry best practice is a double opt-in: After someone subscribes to your list, send a follow-up email with a link they must click to confirm that they want to subscribe.
  • Never buy email lists. Not only is this illegal, it also isn’t an effective way to grow your business.
  • Use real-time address validation. When filling out forms, some people will use fake information — or maybe they’ve just made an honest typo. Either way, you’ll take the hit for the resulting hard bounce. (Want to implement this service? Check out ReturnPath or Xverify.)

In addition, keep your email lists fresh! If your list hasn’t been used in a while, some subscribers may lose interest — making your next email an unwelcome one:

  • Segment your messages. Not everyone on your list will have the same wants or needs. List segmentation enables you to send the right message to the right folks at the right time.
  • Re-engage inactive contacts. These folks clearly aren’t excited by your usual offerings, so consider this a “last chance” to win them over; try sending them an offer they might find especially valuable.

Finally, regularly clean up your email lists:

  • Promptly remove bounced email addresses. This is a requirement of CAN-SPAM.
  • Honor unsubscribes. Again, this is legally mandated — but it’s also common courtesy.
  • Remove inactive contacts. If you’ve got some contacts who simply won’t bite, even for your most enticing re-engagement campaigns, it might be time to strike them from your list.

3. Content quality

As mentioned earlier, spam filters will assess the actual content of your emails.

Also, your recipients might flag your emails as spam if they don’t like what they see. You want to avoid this as much as possible: If too many users file spam complaints against you, your email deliverability will tank. Find out whether you’re a blacklisted sender using

To avoid these situations, keep the following in mind:

Use a familiar “from” name. People are less likely to ignore an email from an individual or organization they already know.

Write a solid subject line. 7 out of 10 people will report an email as spam based on its subject line, making it essential for you to craft something that’s persuasive, yet authentic.

  • Keep it accurate. Nobody likes to feel misled, so make sure your subject line accurately describes the contents of your email.
  • Don’t use all caps. For one, nobody likes to be yelled at. For another, it doesn’t even work — a study by the Radicati Group revealed that people would rather open an email in all lowercase than all uppercase.
  • Don’t use excessive exclamation points!!!!! It’s a classic tactic by inexperienced spammers. Quite simply, you can do better.
  • Don’t use clickbaity, spammy conventions. Phrases like “fast cash” and “100% free” are usually associated with scams. Clickmeter has a comprehensive list of trigger words to avoid.

Compose a high-quality email. Whether rightly or otherwise, certain content types are associated with low-quality content.

  • Link with care: Spammers rely on link shorteners (like to hide suspicious URLs — so use links to your full domain. Also, try to minimize the number of different domains you link to per email.
  • Watch your text-to-image ratio: Using too many images, or oversized images, can make your email appear illegitimate.
  • Clean up your code: Spam filters can tell if your email contains a lot of unnecessary tags — which can happen if, for example, you’ve copied and pasted the text directly from Microsoft Word.
  • Don’t include attachments: Attachments are a common source of viruses. If you must send a file, offer a link that lets your recipient download it directly from your website instead.
  • Avoid rich media: Even if a spam filter lets this content through, most email clients won’t support video embeds like Flash, or dynamic scripts like Java.

Test diligently. Sending a test email is the best way to pick up on deliverability or display issues in advance.

Diversify your content strategy beyond email marketing

Even the best emails sometimes don’t make it past spam filters.

Don’t put all your eggs in one basket — email should be just one part of your marketing strategy. There are other ways to reach a targeted group of people with your marketing message, whether through social retargeting or crafting informative blog content.

Need help refining and diversifying your marketing content? Sign up for the Sprk’d Content Detox: a six-week email course that will get your writing into fighting shape. (And don’t worry — we’ll never send you spam.)

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