28 Tips To Avoid Spam Filters When Doing Email Marketing

28 Tips To Avoid Spam Filters When Doing Email Marketing

If you are in the business of email marketing, you are under the constant pressure of having to think about spam traps, spam trigger words, and anti-spam laws. Crafting targeted emails so as to avoid being sent to spam, or being marked as spam by your subscribers has become an art in itself. Why?

Because Internet Service Providers (ISPs) are waging a brutal, yet justified war against spammers. Unfortunately, the victims are not always just the spammers. Collateral damage happens to include some of us, the good-willed email marketers who simply don’t have the luck or enough experience.

According to research conducted by ReturnPath, only 79% of emails sent by genuine email marketers reach subscribers’ inboxes. How come? Well, only a small error is enough to send an email from an honest email marketer to the 9th circle of email marketing hell, causing serious, almost irreparable damage to email deliverability and the sender reputation.

The seriousness of the issue is evident from the very fact that almost every internet major country has lawfully restricted the use of email spam. The American CAN-SPAM Act of 2004 and Canadian CASL of 2014 (Canada’s Anti-Spam Legislation) represent the leading states’ attempts to protect people from unsolicited, and unrequested bulk mail. Along with the ISPs, they seem to be doing a good job.

So, I would like to present the dos and don’ts of targeted email marketing. This comprehensive guide will help you navigate around spam traps and filters to securely arrive at the desired inbox.

What is Spam traps and Spam filters

ISP’s first line of defense against spammers are spam traps. They are actually email addresses designed specifically for identifying and tracking spammers.

If your triggered email hits such an address, you are immediately flagged as a spammer by the ISP. Your IP address and your ‘from domain’ get blocked, your deliverability rates plummet, and it can take you up to a year to restore a good sender reputation. This is how pure spam traps function. Pretty scary!

Another thing to worry about are recycled spam traps. They are inactive email addresses that ISP acquires after a certain period of inactivity. If your email hits such an address, the consequences are not as serious. Either your ESP or the ESP of your client will send you a notification of the bounce to let you know you are emailing a dormant address. But, if you continue to send emails to hard bounces, the ISP will eventually record it as a spam trap hit.

ISP’s second line of defense against spammers are spam filters, a program that, by using different criteria, filters out unwanted and unsolicited bulk mail, thus preventing it from ever reaching email inboxes. Spam traps scrutinize your targeted emails to the minutest details so as to make sure irrelevant and poorly written content never reaches the subscribers.

Without further ado, here are the things to take care of to avoid spam filters:

1. Pay Attention to Technicalities

There are certain technical issues surrounding the process of triggered email marketing that you can take care of to maximize your email deliverability:

2. Use a recognizable sender name

Use a recognizable sender name

It’s a good practice to always strive to send emails from an email address that contains preferably your personal name with your brand name so that the recipients recognize you.

Why? Simply because in the sea of emails they receive every day, they have to choose which ones to open. And people prefer to open those which include a personal name in the ‘from’ box, rather than impersonal, generic one.

A study by Convince and Convert shows that 43% of email recipients will click spam based solely on the info they see in the ‘from’ field, name and email address.

Email addresses such as firstnamelastname@domain or any variation are always a good choice.

Moreover, leading Email Service Providers (ESPs) tend to pay close attention to the ‘from’ field. Why? Because spam technology also has reputation based filtering that gathers information about the source of the message (IP address and domain) among other things.Changing the source IP address often signals shady business to ESPs. They will alert the ESP to perform a check on you. And if you inadvertently choose a blacklisted address, your email will be filtered out. Ultimately, changing the email address frequently will confuse the receivers that will feel tempted to mark you as spam.

You can prevent this from happening by avoiding:

        1. frequent changes of “from” field names
        2. obscure ‘From’ field names such as: 1258gps@doman; noreply@domain

For example, avoid
Error to Avoid in email

iImage source: tenor.com

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3. Choose a reliable ESP – Email Service Providers

Email Service Providers gain good reputation based on the good reputation of their clients.

If ESP’s clients send out valuable and relevant content and have high scores on their IP addresses, their ESP becomes trustworthy. Steering clear from disreputable ESPs is a must, as their IP addresses usually get blocked by reputable ESPs such as Gmail, Yahoo! Mail or Hotmail.

4. Get a certificate by a third party

There is also a possibility of getting a sender accreditation by a third party that acts as a guarantee to the ISPs that you are not a spammer.

There are companies, like ReturnPath, that assess your email practices and certify you as a trusted sender. This certificate guarantees that your emails will reach a majority of the inboxes you send emails to since it signals to ISP to let your emails bypass spam filters.

This is not a free service but is probably worth investing in since the money you spend can return with increased conversions.

5. Check if you are a blacklisted sender

If your IP address has a bad reputation in the virtual world, your targeted emails are more likely to land in the spam folder. The reputation of your IP address affects your email deliverability rates directly.

There are certain tools, like Multirbl.Valli or MxToolbox, that let you check if you are a blacklisted sender.

All it takes is to enter IP address or domain name in the box, and click ‘check’.

Checking if blacklisted or not via MXtoolbox

6. Test your emails before sending them

It is always a good idea to test your emails before you actually send them to your subscribers.

For example, Mail Tester helps you test the quality of your emails. It mimics spam filters and literally tests for spammyness. The score you get might help you improve deliverability.

7. Always be up-to-date with spam filters technology, ISP practices and anti-spam law

This might seem like a tedious and boring task since it requires you to be constantly alert to the technological changes and the upcoming laws.

However, your constant learning and improvement will only benefit your triggered email marketing campaigns in the long run.

8. Keep email lists clean

To avoid spam traps and spam filters it is essential you keep a good email list hygiene. Here are some tips to help you with that:

9. Never, ever buy email lists!

Purchasing an email list is wrong on so many levels that I don’t know where to begin.

Legally, it represents a violation of your ISP’s Terms of Service. Also, owing to the CAN-SPAM act, selling or transferring email addresses to other lists is illegal. It also represents a violation of privacy of the people whose addresses are on the list as they never accepted to be contacted by you.

Finally, the study from Convince and Convert shows that email lists that have 10% or more unknown user addresses only have 44% of their emails delivered by ISPs!

These lists contain info that is out of date and as such, usually contain inactive or dormant addresses or recycled spam traps. What’s worse is that you don’t know if these lists are harvested. If they are, the chances are they will contain pure spam traps, a one-way ticket to email marketing hell. So stay away from them!

10. Remove hard bounces from your mailing lists

As I already explained, sending a number of emails to an inactive address will eventually be recorded by the ISP as a spam trap hit. Bounce rates are one of the important factors ISPs keep track of to determine your sender reputation. And a bad reputation will damage your deliverability.

Pay attention to the notification of the bounce ISP sends you and delete the problematic email from your list.

notification of the bounce sent by ISP

11. Pay attention to the dormant subscribers

If you notice that some of your subscribers are not opening, reading and clicking your emails, you should act upon it.

Inactive subscribers might damage the reputation of your company’s domain which directly influences deliverability rates. So, either launch a re-engagement campaign or unsubscribe those you don’t get a feedback from.

12. Ask for the subscription twice

Make sure your subscribers really want to hear from you.

Upon subscription, send them another email where you ask them to confirm they do indeed want to receive emails from you. The double opt-in helps you keep your list neat and clean, and your domain reputation pristine.

Ask subscribers to add you to their contact list

This is a simple trick to help you bypass rigorous spam filters.

If a subscriber adds you to their address book, it signals to the ISP that your IP address is whitelisted and that your subscriber wants to receive your emails.

Most spam filters work like this. So don’t be shy and ask them!

13. Respect the unsubscribers

One of the main postulates of the CAN-SPAM Act is that you should provide the unsubscribe option, always.

It’s the law. If people want to unsubscribe, let them go. Make their journey easy by making it a one-step process, and respect their wishes – never email them again.

Insert unsubscribe link in your email

If you continue to send them emails, they are likely to mark them as spam, which will hurt your sender reputation and reduce email deliverability.

iImage source: tenor.com

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14. Take good care of the subject lines

As the old proverb states and a Placebo song, the devil is in the details. This applies to the art of email marketing in general, especially when it comes to crafting subject lines.

As per the same data from Convince and Convert, 69% of the people will mark an email as spam based on the subject line they see. In order to avoid that, make sure not to do the following:


In the etiquette of email communication or any Internet communication, using upper case to write words and sentences is usually seen as shouting, and is considered rude and disrespectful. So avoid using all capital letters in the subject lines.

In the research conducted by the Radicati Group, the majority of the people surveyed, 85%, showed preference of an all lowercase subject line.

Subject lines written in uppercase will not only annoy the receivers, who will feel tempted to mark your email as spam, but it will also alert spam filters.

      1. Don’t use multiple exclamation points

In order to draw people’s attention to your email, it is important to craft a witty, inquisitive subject lines, and a relevant, short email.

As a matter of fact, the research shows that email subject lines that end with a question mark have 44% higher open rates than those that contain exclamation points.

Don’t create drama and sensation by using multiple exclamation points in a row because the chances are they will come across as spammy to the receivers, and to the ISPs.

16. Stay away from spam trigger words

Spam trigger words - words that considered span in email

To avoid hitting spam filters and getting caught in them, pay attention to the wording of your subject lines.

Certain words and phrases, such as ‘free’, ‘best price’, ‘cash’, ‘no obligation’ have been blacklisted owing to their association with the spam mail. Recall all those emails we used to get that offered a free prize in the subject line in return for following a couple of steps of which you learn once you open the email.

Spam trigger words were usually collected from emails such as these, and should be avoided.

Ultimately, HubSpot offers these as examples of the good subject lines:

“Hi [name], [question]?”
“Did you get what you were looking for?”
“You are not alone.”
“Feeling blue? Like puppies?”

17. Don’t make false promises

In order to avoid being marked as spam, it is important to align the subject line with what you offer in the email. In other words, avoid writing spammy emails described in the paragraph above.

If your subject line states: “Hello Jovana, a quick question?”, then indeed do include a short question easy to answer to. Deliver on what you promise in the subject line. Because, if your email copy doesn’t correspond with the offer in the subject line, it is more likely people will mark your email as spam.

18. Take good care of the email body

Spam filters rigorously scrutinize your copy as well. ISPs go as far as to mark emails as spam based on the specific content or images.

Everything matters, the design, the fonts, the attachments, the embeds, the images, everything. Even the most bizarre things, such as using the word ‘viagra’, can alert the spam filters. The devil is in the details, and here, the best policy is to keep the details to the minimum and to simplify, as much as possible.

Here are some tips on how to craft an email copy that’ll bypass the spam filters and appeal to your subscribers:

19. Avoid rich media content

A majority of email clients don’t allow the ability to view rich media content, such as video embeds and Flash, so avoid putting them in your emails.

If you do insert them, and they don’t show or work properly, it will seem sloppy and messy to your clients. This can damage your credibility as the email will seem spammy.

If the media content is essential to your marketing campaign, put it on your website and insert a link to it in your copy. For example, if you want the subscribers to see a video, include an image with a play button that, once clicked, will lead your clients to the particular video on your website.

Also, avoid using JavaScript and other dynamic scripts, as they will alert the spam filters.

Your clients usually don’t allow the dynamic scripts to function, so using them will create pretty much the same effect as the media content that doesn’t show properly.

20. Avoid embedding forms

Embedding forms in your email copy represent another red flag to the spam filters. Forms represent a security risk and aren’t usually supported across common email clients.

Instead of including embedded forms, you can either link to the page you wish them to visit, or insert a call-to-action button.

21. Avoid including attachments

Attaching files to your emails, like Word documents or PDFs, alerts spam filters immediately. Attached files also increase the size of your email, so consequentially, it takes them longer to load.

You can bypass this by placing the particular document on your website and providing a link, or a CTA that leads to the document’s location.

22. Tone down the fonts and colors

People seem to pay a lot of attention to the fonts and colors used in the copy. In the previously mentioned Radicati Group study, over 60% of the people surveyed found it unacceptable if the email marketers used irregular fonts, different font sizes and font colors. And over 70% of people declared that they prefer one size fonts.

Here’s an example taken from HubSpot that shows what NOT to do:

avoid Excessive font and color in email

Irregular font colors and sizes also alert spam filters, and the same goes for invisible text (white font on the white background for example). So simplify!

23. Cut back on the images

Even though we live in an era where pictures and images dominate all spheres of life, it seems that in email marketing you can have one too many.

Including a lot of images, or big images will increase the load time of your email, which can affect deliverability rates.

Making your copy in the form of one big image will also probably get it stuck in spam. For example, Microsoft Outlook doesn’t recognize background images so an email like this will probably not be displayed correctly:

Image based email - image relevant to the content

To avoid this, make sure to include images that are relevant to the content and complement it. Resize the images if necessary, but take special care not to damage their visual integrity. And always, always, host your images at credible services.

24. Make sure your images display correctly

Some email users allow the display of images while others block images altogether. Your images won’t show correctly to the users who block images, which will make your email seem spammy, messy and sloppy.

To avoid that don’t miss to add intelligible, unambiguous alt text in your image. This is how alt-text looks like

Alt text in the email image

SourceAlt text can be easily edited and can also be added with custom variables as apparent in the above image.

25. Offer both plain text and HTML

Take time to craft both a plain text and an HTML version of your email. The former allows you to be plain and simple, the latter lets you loose your inner designer (just don’t overdo it).

This way, you appeal to different people, but you also establish your legitimacy with the ISP.

Make sure that your code is correct. If your email includes broken or incomplete tags, the spam filters will probably prevent it from reaching the desired inbox.

26. Correct spelling and grammar

Spell-checking and proofreading are essential components of every good email marketing campaign. Incorrect spelling and faulty grammar will damage your credibility with your clients and make you seem unprofessional.

The Radicati Group study shows that 80% of the people surveyed find grammar and spelling errors a capital emailing offense. It makes you seem unreliable and untrustworthy.

These errors are also major spam triggers. So do take the time to edit and proofread.

27. Make it easy to unsubscribe

I have already mentioned the importance of offering an easy way out of your emailing campaign. It’s the law, and it’s a good professional practice.

Include an unsubscribe button or link in each and every one of your emails. Thus, you protect your reputation and credibility with your clients and the ISP.

28. Take care of the follow-up

Never send emails just to send them. Try to offer valuable, engaging and relevant content because this is probably the only way to avoid being marked as spam.

A steady flow of communication is important if you are following up with your clients or if you are trying to re-engage the inactive ones.

Instead of opting for massive blasts (that tend to reek of spam) that you send from time to time, try to space them evenly, after shorter periods of time, just to remind your clients that you are there.

This way, you will have a firmer grasp on the inactive ones, preventing them from cluttering your email list or becoming possible spam traps. And the active ones will appreciate your effort and value.


Unfortunately, there is no magic formula that guarantees your emails won’t land in spam. ISPs, ESPs and anti-spam laws are brutal, and there is no definite guide to help you deal with the deliverability issues.

By paying attention to technical issues, cleaning email lists, taking good care to avoid all spam triggers in the subject lines and email bodies, and by following up appropriately and in a timely manner, you are more likely to preserve your credibility, sender reputation and protect your IP address and domain from ever getting blacklisted.

As spam technology is everything but solid ground, I would love to hear your input, experiences, and comments, so feel free to comment.

iImage source: tenor.com

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  • Created: 15 Sep 2017
  • Last Updated: 01 Jul 2019



Jovana Petrovic Researcher, Etools

Jovana is a writer and a researcher at Etools – a toolkit that lets you find the exact contact details of any business.

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