35 Tips on How to Avoid Spam Filters in Email Marketing

With over 6.5 billion email accounts in the world – and rising – email is not going anywhere. Additionally, considering most people prefer to receive commercial communication by email, email marketing isn’t going anywhere either. That’s good news. (Great news actually, since email marketing on average yields 3800% ROI.)

So then, what’s the not-so-great news? In a word – spam.

No, we don’t mean the genuine email marketer sends out spam. Far from it. However, many unscrupulous people do send out spam. As a result, fulfill marketing emails, with legitimate value, can sometimes be lost in flood.

That’s why, at some point, every email marketer worries that their carefully crafted, beautifully designed newsletters could potentially land up in the spam folder.

What is Spam?

For the average email user, spam is the unwanted email that clogs up their inboxes. However, the definition is more nuanced than just unwanted email, and it is essential for an email marketer to know, so you don’t accidentally create a spammy newsletter.

Spam emails are those communications that fulfill 2 main criteria: they are unsolicited and are sent in bulk. Other factors include those with malicious intent or ones sent from anonymous addresses. Also, there is rarely a way for a recipient to opt out of further communication, even if the messages are irrelevant for them.

What is sending reputation?

There are many factors that affect email deliverability, but perhaps one of the most critical ones is a marketer’s sending reputation, sometimes also known as their sender score.

A sender score assigns a percentage to the likelihood of the sender using good email practices: sending wanted mail only, pristine lists, and so on. An ISP assigns a sender score based on email campaign metrics too, like clicks, bounce rate, and unsubscribes.

So what does the sender score signify? ISPs use sender reputations to determine whether an email belongs in the inbox, or the spam folder. Basically, the higher the percentage, the better your sender score, and consequently, better email deliverability for your campaigns.

Sending reputation is also evolving with time, and now comes in two flavours: IP reputation and domain reputation.

IP reputation was previously the de facto standard, but as ESPs can use the same IP for multiple companies, both positive and negative consequences affect all companies. Therefore domain reputation has emerged, where the score is tied to the domain, which is generally a company’s brand.

Sender score

Tip: There are several free services that can measure your current sender score, and thus give you an idea of your current status. Return Path’s Sender Score is a favorite amongst email marketers. Alternatively, there are services by internet security organizations, Barracuda and McAfee.


35 tips to avoid the spam folder

We’ve already waffled about a lot about the subject, so let’s get right to the brass tacks.

The right kind of email list

1. Only send emails to people who have opted to receive your emails: Also known as permission-based email marketing, this is the only real way to build your email list. It may seem incredibly tempting and much easier to gather email addresses from other sources, but that strategy will inevitably ricochet back on you.. 80% of social media contacts receive unsolicited email.

In fact, to make entirely sure that someone really wants to be on their mailing list, companies adopt a double opt-in system. If someone signs up for a newsletter, they must confirm their subscription via a link sent to that email address. This is to weed out inadvertent signups, potential errors, and unauthorized uses of email addresses.

Tip: We can’t emphasize this enough – don’t buy email lists. It is just not worth the risk, and some ESPs will outright ban customers who use purchased email lists.  

2. Clean up your email list regularly: Contacts will sometimes go cold; this is a reality of email marketing. Perhaps the contact was engaged before but isn’t opening emails any more, hasn’t visited the website, nor have they transacted recently.

Assuming all engagement campaigns have fallen on figurative deaf ears, then it is time to cut them loose because a persistently unengaged subscriber will impact your metrics negatively. Unenthusiastic responses to email subscriptions trip spam filters. The same logic applies to contacts whose emails register as bounces. Get rid of them.

Sometimes contacts opt in to receive emails, but never actually open them. This sort of email is known as graymail.

Why do you need to know this? Well, ISPs look at graymail with suspicion, and tend to send unopened email to the junk folder. It also affects your sender score.

3. Age matters: Email addresses are subject to change, as people switch jobs, move countries, or delete accounts. If you haven’t contacted the email addresses on your list for over a year, then it is best to check whether they are still in use before sending them any marketing emails. About 30% of people change their addresses annually, so older email addresses have a greater likelihood of returning hard bounces or, worse, they could be spam traps.

4. Warm up your IP address: Are you bringing in email marketing for the first time? That means you have a cold IP address, and you are an unknown sender for the moment. Thanks to the plethora of nefarious spammers who switch addresses at the drop of a hat, cold IP addresses are guilty until proven innocent.

Therefore, you must start warming up your IP address. Start by sending emails to a core group of dedicated contacts, who will show your newsletters lots of love – open them, click on links, and be engaged. Thereafter, steadily increase the number of essential.

Consistency is key

5. Send email responses to customer actions quickly: Any time an email communication needs to recognizable to a customer, like with a welcome email or a transactional email, it is best to send the email immediately. If you wait too long to respond, subscribers may forget about the subscription and that may result in unopened emails, which impact numbers.

Welcome Email | Firefox

6. Keep the volume of sent emails steady: When scheduling your newsletters, try and keep the numbers you send out each time steady. For instance, if you have 10,000 contacts on your email list, and you are emailing them in tranches, break up the total evenly over time slots. Don’t send out 50% the first time, and then 2%, and swing back up to 45%, and so on. It sets off alarm bells with ISPs.

7. Send emails regularly: Just as the volume should ideally be consistent, so too should the frequency of emails. Suddenly switching from the rare email once in 6 months to a battery of newsletters in a week will raise red flags. If you want to change up the frequency, do it slowly, and ease into it. Vice versa, don’t abruptly stop email marketing and then restart several months later, expecting to pick up where you left off. ISPs don’t like that at all.

Send emails regularly

8. Stay on brand: When designing advertising, companies have set brand colors, fonts, designs, and logos, among other marketing collateral. Rarely do they deviate from these presets, knowing that brand recognition is built from multiple elements. Email marketing is no different. Consistent designs boost recognition for contacts.

Branded email | AWS


Content is everything

9. Keep the image-to-text ratio sensible: It is very tempting to design a pretty newsletter, and send it as an image. That way, your beautiful design cannot be wrecked by mismatched fonts. But spam filters cannot read images [yet], and so tend to block emails whose content they cannot assess. So, keep the beautiful design for sure, but type in enough text to explain the images adequately too.

10. Short and simple: Even though shortening attention spans are a contentious topic, the reality is that your emails are competing within flooded inboxes with loads of information that needs to be processed. If you have a message to convey, you don’t want it to be lost in the deluge. Plus, excessively long emails trigger spam filters. Basically? Keep it short.

keep emails short and simple

11. Keep content relevant: To keep contacts engaged with your brand and your campaigns, ensure that the content in your emails is relevant to their interests.Use analytics to keep track of previous behaviour and engagement, and to tailor campaigns. 67% of contacts unsubscribe because of irrelevant emails.

Relevant content in email

12. Use lowercase or sentence case: Possibly because Internet etiquette perceives all caps as “shouting”, using it in marketing emails is a clear no-go. In fact, over 85% of people prefer email subject lines entirely in lowercase. Besides, shouting is impolite.

13. Avoid spammy keywords: Open your spam folder, and you’ll see trends emerging amongst the subject lines there. Subject lines that scream enhancement, lotteries, medications, prizes, money, and much more. [In all caps and with lots of exclamation marks too.] Spammy keywords are triggers for spam filters, and thus should be avoided as far as possible.

However, there is a caveat here: sometimes they are relevant to the message you want to convey. Therefore, context is essential. Try using more neutral language instead of attention-grabbing copy.

14. Proofread everything: Professional emails, even if they are written in a casual, conversational tone, should still ideally adhere to proper grammar and spelling standards. While the odd typo won’t cause the apocalypse, spammers deliberately misspell words to trip up filters, and as a result, spelling mistakes are now spam triggers.

15. Cleverness is good, in moderate doses: Subject lines are forced to bear much responsibility for the success of a campaign. Open rates and sometimes even unsubscribe rates are pegged to them.

Although market studies results have varied over what works, one common thread has emerged: subject lines that describe the email contents accurately each time are the best. This may seem obvious, but often emails have mysterious or “interesting” subject lines, which give out no clue as to the contents of the email. That strategy works well on occasion, but not as the norm.

The human touch

16. Use natural language: This point is slightly subjective but still needs to be made. Avoid using overly complicated language to convey your marketing messages. Quite apart from potentially alienating contacts, phrases that confuse users confuse spam filters too. Confusing a spam filter is tantamount to being junked.

Human touch in email

17. Send email from a most prominent name: Contacts tend to junk email based on whether they recognise the sender. The subject line comes later. Using either your company brand or a real person’s name in the sender field builds upon familiarity in a contact relationship. 42% of contacts decide to open emails based on sender names.  

18. Ask subscribers to whitelist your address: This is a sure-fire way to make sure subscribers get your emails because ultimately they decide what comes into their inboxes. If a subscriber adds your email to their address book, spam filters will respect that decision.

19. Check in with your subscribers: The best way to find out what your contacts want is to ask them. Occasionally, consider conducting your own market research, asking questions that elucidate your analytics. Ask for feedback on email frequency, content, and more to remain subscriber-centric.

take subscriber's feedback

Marketing Automation is your friend

20. Use personalization: Spam filters screen content to look for indications that you know the email contact. Generic emails tend to be flagged as unwanted email, and thus have a greater chance of landing up in the spam folder.

Use personalization in email

21. Use segmentation and dynamic content: In case you have several different segments in your email list, use that information to create highly targeted campaigns that tailor to each segment’s interests. Segmentation is far more effective as a marketing tool, when compared to a one-size-fits-all approach and translates into increased engagement and conversion.

22. Get insights from your analytics: Learn to read between the lines with analytics. You will find patterns in the data, explaining why an email campaign was successful or not with a certain segment of your audience. Use the information to improve your content constantly, so that you are always delivering relevant content, and thus ensuring high engagement and improved chances of conversion.

23. Test test test: Regardless of how many studies you read – ideally you should read a lot of them – none of them will know your subscriber base better than you do. Have different variations of content, subject lines, CTAs and so on to see what works best with each segment. 

User experience is very important

24. Responsive emails: Almost 60% of email opens occur on a mobile device. Analytics of your campaigns will eventually bear this fact out, so make sure your emails render well on all screen sizes. For instance, having horizontal scroll bars on a mobile screen is annoying. Make buttons easy to find on smaller screens too. Responsive design has a huge impact on user experience, and you want to ensure your contact has only the best user experience possible.

25. Test test test [part 2]: Different email clients and providers render emails in different ways. Your email could look exactly the way you want it on Gmail, but be completely messed up on Outlook. Test emails on a battery of applications, clients, and devices to make sure your contacts are getting what you intend to send them.

26. Make meaningful font choices: Spam filters flag emails that use too many fonts, too many colors or too many sizes for text. Another font-related trick that spammers use frequently to trick people is ‘invisible text’, which is essentially white text on a white background. Another red flag for spam filters, and poor design choice overall.  

27. Avoid attachments: It is tempting to send richly informative emails, with videos and PDFs, all carefully crafted into one big campaign. But some email servers don’t even allow attachments with emails. Videos trigger spam filters. Heck, big images trigger off spam filters!

Put a teaser in the email, with adequate explanation and appropriate context. Have clear CTA buttons taking contacts to a website with all the multimedia messaging your marketer heart desires, and you’re golden.

28. Forms don’t belong in emails: Just nope. CTA to form hosted on a webpage. That’s good user experience right there. [And your developer will thank you.]


29. Choose a good ESP: Just as email marketers have sending reputations, so do email service providers. They have established track records with several ISPs, and thus their servers already have good reputations. Additionally, in case an email hits a spam trap and lands the sender on a blacklist, the ESP can intervene and sort the issue out on both sides. Quite often, support teams will provide advice on how to clean email lists and generally establish better campaign practices.

30. Send emails from your own domain: Your domain is tied to your brand name, and your sending reputation. A free email service like Gmail or Hotmail doesn’t carry the same weight for a contact or an ISP as a domain name. Additionally, you want your brand to be associated with credibility, as you are building a reputation for good email practices.

Tip: The advantage of domain-related reputation is that, in case you ever decide to change ESPs, your reputation is carried with your domain, and thus you do not have to start again from scratch.  

31. Authenticate your emails: In order to combat phishing attacks – which is when malicious users mimic your domain to scam your contacts – authenticate your domain and emails. Doing this signals ISPs that your emails are genuinely being sent from your domain – by you and no one else – and can be safely delivered to users’ inboxes. Two main protocols exist: SPF and DKIM. It is bit technical but well worth the effort to boost your sending reputation.

32. Timing can be critical: We’ve talked a lot about making sure people engage with your newsletters, and how to ensure content is great. However, you could be sending the best emails ever, but just not at the right time. Therefore, they remained unopened. Use analytics to figure out the best time to interact with your contacts, and incorporate that insight into your campaigns.

time critical email

33. Comply with compliance: Regulations now focus on protecting the privacy and data of individuals, and stringent measures have been put in place for companies. It is really in a company’s best interest not to run afoul of compliance regulations, so always stay within the lines of those.


34. Let people unsubscribe easily: We get it. It is hard to let go of a subscriber. But, despite that, don’t make it difficult for contacts to unsubscribe. Have an easy to find an unsubscribe button or link, and take them to a survey to convince them to stay or hear their reasons for leaving. If a contact can’t unsubscribe easily, they are going to mark your email as spam.

unsubscribe option in email

35. Unsubscribes are sacrosanct: There are going to be times when a subscriber changes their mind about your newsletters. It is sad, but honoring their wishes is not negotiable. You can try changing their minds with an effective unsubscribe page, but thereafter their email comes off the list.

Extra reading

Why is spam such a big issue?

Spam almost always has malicious intent. Email address lists are gained from unscrupulous sources and aims to defraud the recipient off their financial or personal information for gain.

While most individuals with adequate exposure and familiarity with the Internet would not fall for email-based scams, there are still those that do. Even if one person falls for a scam, it justifies the negligible cost incurred by a spammer.

Spam accounts for 14.5 billion messages per day. Thus regulation, by email service providers and lawmakers, has come in to protect individuals from spam.

Spam fighting techniques

Email service providers [ESPs] care about restricting spam in their users’ inboxes because spam adversely affects the user experience. It is in their interest to ensure that their customers – even non-paying users are customers – have the best user experience, in order to ensure that they continue using their services.

There are a host of techniques to keep spam out of inboxes. We’re going to look at a few salient ones.

Spam filters

Filters are a set of rules through which emails are passed, before being delivered to the right email folder. They can be applied in a few ways, right from inbuilt protocols by ESPs, or even third-party software that integrates with email clients.

Mostly spam filters check incoming email messages for content and falsified header information. Algorithms check email messages against thousands of criteria, assigning values to the probability of the email being spam. Then there are some filters that require recipients to authorize senders before receiving email communication from them.

Content arguably plays the most prominent role in spam filtering, right from the header to the footer, and everything in between. Sender reputation is also vitally important to ensure deliverability.

Spam traps

Spam traps are email addresses that aren’t associated with a person, and are used to catch spammers unawares. There are two types of spam traps: pure traps and recycled ones. The distinction is important, because even the most conscientious email marketer can inadvertently hit a spam trap.

A pure or pristine spam trap is one that was never owned by a person at all. These are created by ESPs or blacklist operators to collect email and IP addresses of spammers, and then used in spam filters. These email addresses are not given out, so the chances of them landing on a legitimate mailing list is negligible.

A recycled spam trap is an email address used to belong to an individual but has since reverted to the service provider. Thus, the user may have used the address to sign up for a mailing list at some point. Hitting a recycled spam trap is not as severe as hitting a pristine spam trap, but indicates to ESPs that the mailing list is not up to date or not used frequently.

Spam traps are serious, and have an adverse impact on deliverability and sender reputation. Therefore it is good practice to keep email lists updated regularly to weed out unused or abandoned mailboxes.


Focus on improving your sending reputation, and remember it is a slow-won battle. Keep track of policies and regulations, ensuring your email marketing is always subscriber-centric. These two maxims will stand you in good stead and reward you in the future.

Have we missed any important points? Share your thoughts in the comments!