Oct 04, 2016 / by Jim Dougherty

Nearly any digital marketer will tell you that email is a preferable communications platform compared to social media. Delivery rate is higher, open rate is higher, click-through rate is higher… it’s not a controversial assertion (although the barrier-to-entry for email is more difficult than most social platforms).

Spam filters aren’t discussed enough in the context of digital communications and marketing (specifically, avoiding spam filters).

We take for granted sending an email to a subscriber and them receiving it, but if your message is quarantined in a spam filter, your messaging is going to be significantly diminished. Especially if you get blacklisted by one of the major email service providers (ESPs) such as Gmail, Microsoft, or Yahoo, which control large percentages of the email market.

What I want to do in this post is to discuss the reasons why your email could get caught in a spam filter and how to triage that situation if it happens.

Algorithmic versus Manual Flagging

First, let’s start by defining spam as “unsolicited or undesired electronic messages.” We generally think of spam as unsolicited, but by adding “undesired” we also introduce a subjective aspect to spam prevention. You may have opted-in to an email list and then received messages you don’t want – this is spam. This is important when we consider how spam is identified and filtered.

There are two methods of spam identification: algorithmic versus manual.

Algorithmic identification is an automated flag of a content element within your email that shares characteristics with other spam.

Manual identification is the reporting of spam content by users who received it.

Once you’re flagged as a spammer on an ESP, you have a lot of extra headaches to get off of their “blacklist.” Different ESP algorithms consider different variables and ESPs will have different users, so it’s completely possible to be identified as spam for one ESP and be clean on the rest.

My personal domain was blacklisted by Microsoft after it was inserted as the PR contact for a philanthropic organization who liked to email a lot to a list that may not have been as opt-in as they intimated. This was likely a manual flagging.

I also had an incident where one of my Gmail accounts was rejected by Barracuda as spam after I responded to a few emails in their protected domains with short, indistinct notes. This was likely an algorithmic flagging.

Either flagging scenario is frustrating. Let’s dig a little deeper into how you can avoid getting your email flagged as spam.

Avoiding Spam Filter Algorithms


We don’t know the exact variables considered by ESP spam algorithms, just like we don’t know exactly what goes into a search algorithm. But marketers see trends over time, and this is a list of common items that are suspected to trigger spam filtering. Algorithmic filtering also provides you with feedback, generally in the form of an undeliverable note from an ESP. So, when you’re in trouble with an ESP you should receive messages to that effect.

CAN-SPAM Compliance

When looking at algorithmic flagging we have to make assumptions. One of easiest assumptions to make is that algorithms are going to check your compliance with the CAN-SPAM act of 2003. There are six key requirements of CAN-SPAM that you should be aware of:

  • No misleading header info
  • Subject line should not be deceptive
  • Identify the email as an ad if it is promotional in nature.
  • Provide the physical address where the email is being sent from
  • Tell recipients how to unsubscribe from the list
  • Honor opt-outs promptly

Because these criteria are explicit, at a minimum your email should comply with these. Beyond the obvious, there are other “flags” that are presumed to trigger spam alerts for many email service providers.

Link Reputation

An easy way for an algorithm to judge the quality of an email is the quality of the links that are contained in the email (especially for ESPs like Gmail, Outlook, and Yahoo which have similar algorithms in place for search). Of course, you probably have to live with the reputation of your business website, but you can control the other links that you use in your email.

There are multiple ways to check the quality of the link you’re using, from a simple Alexa search to an earnest reflection of the link from every conceivable angle.

In any event, the key to link reputation is how the ESP perceives link reputation, not your personal opinion. For example, I personally think that 90s pop star Joan Osborne is more enjoyable to listen to than Rihanna. Joan Osborne’s site is ranked 4,050,480 in the world according to Alexa, Rihanna’s is ranked 203,449.

My personal opinion is clearly outside of the mainstream view according to site popularity, and that’s more or less how link reputation works.

Do this instead: try to exclusively use “Rihanna”-quality links.

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Use Smaller Lists

Many email marketers recommend batching your email blasts into smaller lists. You may already do segmentation of your subscribers, but the intention of this batching is to diminish the volume of spam reporting per email sent. It depends on how ESPs determine trustworthiness, but it’s worth trying (especially if it has worked for others).

Do this: Segment your mailing lists; A/B test where appropriate and batch your messages into smaller groups.

URL Shorteners

Long story short – don’t use these. I know this has probably never happened to you, but sometimes URL shorteners send people to dubious destinations. Many ESLs assume that URL shorteners are used for nefarious purposes even if your intentions are pure.

Do this instead: use normal URLs when you include links.

No Javascript, Code, Video, or Embedded Forms

Speaking of nefarious purpose, there’s a pretty narrow expectation of what an email is expected to do (both by people and by ESLs). Extraneous code, video, and embedded forms (presumably using code for submission) are generally seen as dangerous by ESLs and are almost always sent to the spam folder.

Do this instead: use email as a communications device and be wary to do more than the channel allows you to do.

Text Only = Okay. Text + Image = Okay. Image Only = Not Okay

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One of the more prevalent types of email in my spam folder are images without text. You’d like to give people benefit of the doubt about a lot, but images in lieu of text indicate a fairly obvious attempt to obfuscate messaging.

Do this instead: Use your words (complement with an image if appropriate).

Don’t Use Verbatim Text From Your Content For Your Subject Line

This is probably a less common trigger; however some analyses have noted that headlines using verbatim quotes from the body of your email may be flagged as spam.

Do this instead: Paraphrase or come up with something original for your subject line (A/B test different possibilities perhaps?).

Use Uniform Fonts…in Black

One tactic that nefarious email marketers have abused in the past is to use white-colored text in their emails (making them transparent to the recipient) and a bunch of different fonts (presumably to distract from something else). Perhaps you are not diabolical, yet have extraordinary panache that you express with email colors and fonts. You must suppress your panache for the sake of your deliverability.

Do this instead: Choose one font and stick with it. Use a consistent, visible text color (black, for example).

Don’t Send Your Email From a Free ESP

Sinister spammers can’t use their work email to send out blasts, so they create fake accounts on free ESPs (Gmail, Yahoo, Outlook) to mask their true identities. While you have far more honorable intentions than these spamming miscreants, an algorithm may flag you for using your Gmail account instead of a business email. Algorithms can generalize like that.

Do this instead: Send your email (or set your reply-to address) to an ESP that doesn’t offer free accounts.

Use Plain Text and HTML

Simultaneously sending a plain text and HTML version of your email is a way to optimize for mobile, specifically for clients that cannot accommodate HTML. It is probably not a huge discriminator for spam, but sending them in plain text and HTML demonstrates sophistication that spammers rarely incorporate into their email.

Do this: find out whether you are sending both versions in your emails, and if not figure out how to.

Consider Third-Party Certification

There are a few companies that offer third-party certification for email, communicating to ESPs that you are who you say you are (It is like TSA Pre-check for email marketing). These services cost money, but so does having your email quarantined to the spam folder.

Do this: consider whether a third-party certification is worth the investment.

… Or Do-It-Yourself


Ryan Sullivan of WP Site Care writes that you can configure your Sender Policy Framework (SPF), Domain Keys Identified Email (DKIM), and Domain-based Message Authentication, Reporting & Conformance (DMARC) protocols manually. These are all methods to communicate that you are who you say you are… and they are free to implement. However, double check these carefully as configuring server TXT records can be unforgiving (I speak from experience).

Do this: Implement SPF, DKIM, and DMARC. These are low-cost ways to authenticate your IP address and to stay out of the spam filter.

Avoiding Manual Spam Filtering

Phew! That was a lot of stuff to consider about algorithmic spam filtering. Remember that we have to look at how people react to our emails as well. The subjective aspect of spam is put to the test each time you push send. Let’s take a look at some ways that you can avoid being labeled a spammer by the people on your subscriber list.

Let’s take a look at some ways that you can avoid being labeled a spammer by the people on your subscriber list.

Opt-in Only

I know this is a part of CAN-SPAM but it bears repeating: only send to people who have voluntarily opted into your subscriber list. People purchase email lists or send unsolicited messages to people that they know and the results are disastrous: a lot of the recipients report these emails as spam. Of course, this can lead an ESP to label you a spammer.

Do this: Exclusively populate your email list with opt-in subscribers.

Try a Double Opt-in

Have you ever subscribed to a mailing list and received an email asking you to confirm your subscription? This is known as a “double opt-in,” and is becoming increasingly commonplace for email marketers. The downside to this tactic is that is could potentially decrease the number of subscribers that you receive, but there is also evidence that customers that affirm their subscription are more vested in opening your messages and less likely to report them as spam.

Do this: consider whether a double opt-in might be an appropriate tact to verify subscribers to your mailing list.

Add to Address Book

Frequently when you subscribe to an email list, you’ll get an autoresponder message asking that you add their email address to your address book. The reason for this is pretty straightforward: most ESPs won’t send a message to spam if the sender is in the recipient’s address book. This is also described as “user-level whitelisting,” although the general term “whitelisting” is often associated with ESPs.

Do this: consider asking subscribers to add your email address to their address book.


Purge Your Subscriber Lists

You’ll see open rates and bounce rates when you send your email and can break those down to the granular (recipient) level. You want to purge people who aren’t opening your email and here’s why: people who aren’t reading your email are most likely to report your email as spam. As for eliminating “bounces,” ESPs consider bounce rate when assessing your trustworthiness. The thought being that the higher the bounce rate, the less likely that the recipients have subscribed.

Do this: be a discriminating email sender and purge the people who aren’t opening your emails (and bounces) from your lists.

Send Good Stuff

So far we’ve discussed a lot of technical things that you can do to avoid being reported as spam, but there’s one aspect that may be the most important of all: send quality content to your subscribers. You could follow every recommendation in this email or elsewhere and still be considered “undesirable” if you don’t send useful content. We’ve all signed up to a regrettable email list only to get poor content delivered to us far too frequently – don’t do that.

Do this: don’t get so caught up the technical aspects of email that you lose sight of the most important aspect of this type of communication: making content that is valuable for the recipient.

What You Can Do If Your Emails Are Being Filtered

So, what do you do if you’re getting bounced messages or if someone tells you that your email is being sent to their spam folder? Don’t feel bad, a lot of good email goes to spam (political ads **cough**). Let’s take a look at the options once an ESP blacklists you.

Use An Email Solution

One of the more common ways to avoid blacklisting is to use an email solution like Cision’s iContact. These are paid services that handle a lot of the compliance issues and whitelisting that you would otherwise have to do manually, in addition to providing segmentation tools and analytics to help you create more effective campaigns. If you’re blacklisted, the customer support teams for these types of companies can be very knowledgeable about how to restore your IP to good standing with the ESPs.

If you’re using basic tools (like a mailing list distributed via bcc), it is worth taking a look at the features that email marketing solutions offer.

Set-up Test Accounts

Writing for KissMetrics, Maciej Ossowski recommends setting up your test accounts on the leading ESPs such as Gmail, Outlook.com, and Yahoo, to check messages for deliverability on these platforms. If a message goes to spam during a test, it may save you time and effort to troubleshoot span issues before you send the message to your subscriber list. This can also help you narrow any deliverability issues down to particular ESPs.

Test With Text

When you have a spam problem, it may be worthwhile to send a text-only email to your test accounts. This is to verify whether the problem is algorithmic or manual. If a text-only email goes through and an HTML email doesn’t, it can clue you to the fact that there is an element in the HTML that is triggering the algorithmic spam filter. If the text only email goes to spam, the odds are that your domain may be blacklisted and you’ll have to request to be whitelisted (or removed from the blacklist).

Request Removal from Blacklist

Some ESPs provide resolution for ISPs on their blacklist (for instance Microsoft does, but Gmail says to wait until you get a better reputation). If you’re at this point, you’re restricted by what the ESP allows you to do. Once you request removal, it may be a matter of weeks before the whitelisting is approved (this is my experience).


Email marketing and communication is one of the most reliable platforms in the digital sphere. But being identified as a spammer can influence the effectiveness of this channel to accomplish what you want to achieve. Hopefully, this gives you an idea of things that you can do to keep your email communications as efficient as possible: avoiding algorithmic mistakes and manual misunderstandings.

Get more tips that will prevent your content from being ignored with our free guide 3 Stages of Expanding Your Content’s Reach: Creation, Distribution and Amplification. Download it now for step-by-step instructions to:

  • Create momentum for each story’s journey with a distribution roadmap
  • Earn audiences’ trust and loyalty by providing them value
  • Establish authority and expand reach with multi-channel sharing tactics

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About Jim Dougherty

Jim Dougherty is a featured contributor to the Cision Blog and his own blog, leaderswest. His areas of interest include statistics, technology, and content marketing. When not writing, he is likely reading, running, playing guitar or being a dad. PRSA member. Find him on Twitter @jimdougherty.