How To Avoid Email Spam Filters – Ultimate Tutorial

By Peter Nyiri | Email marketing

May 14
email spam

If you’ve been sending emails, you already know that your emails may go to your recipients’ junk folders. Did you know that this may have nothing to do with spam?

Avoiding your emails going to junk folder is one of the most complicated parts of email marketing, such as when you want to promote your online course.

The first thing you’ll may notice is a rather weird behavior. When you send emails to Gmail accounts they are correctly delivered, while with Hotmail accounts they’re marked as spam. This suggests the first important consideration: mailbox providers adopt different techniques to decide when an email is or isn’t spam. Even when you send from a personal domain, there is no guarantee.

The Three Main Factors of Spam

If your emails are going into the spam folder, the first task is to determine what category the problem falls into. There are 3 distinct categories for the cause.

  1. Server or IP address
  2. The setup of sending your emails
  3. Email content

To make things worse, your email client may not tell you the truth. As an example, in this case you may get the idea that the problem is content-related, however that isn’t the case.

similar to messages spam filter

Server/IP Address Problems

Listed In Spam Database

Several web hosting servers have been misused by spammers to send out unsolicited mail to users. For this reason, their IP addresses are marked as spam. If you are on a shared web hosting provider, you may experience this problem. It could be a good idea to get yourself a VPS or a dedicated server hosting because you will be allocated a unique IP. It is easy to verify if this is the problem.

As an example, I have recently purchased a cloud server and I also purchased an expired domain to run the server with.

Then I set up a website on the server, using a different domain.

The below screenshot is from MX Toolbox.


The screenshot shows that the reason why this domain is in the SpamHaus database is because the IP address was listed.

But why was the IP address listed?

Because the hosting domain was listed and for that reason the IP address was marked:



I had to go to the SpamHaus website and request the removal:

Spam DB removal

The first thing I was asked to do was to provide a domain email address and click on the verification link.

spam DB verification email

Then next day I received an email:


This domain has been around since 2012 and has been listed for much of that time.
Did you, perchance, buy this on 23rd April?

After this, the domain was removed.

I did a similar request for the IP address.

Reverse DNS Lookup

If you have professional hosting, this probably isn’t an issue and you can skip this. However if you have your own VPS, you need to watch out for this.

While in the domain DNS zone the hostname (such as is pointed to an IP address, using the reverse zone makes it possible to tell what the hostname from an IP address. There is a so-called PTR record that is used for this reverse DNS (rDNS) lookup.

This procedure provides trust that the given hostname or a domain are connected to the IP address. The PTR records are must have for outgoing mail servers, because most of the mail providers reject or mark as spam messages received by mail servers without valid reverse DNS configuration (missing PTR or if the PTR record and hostname IP address don’t match).

In my case the server domain resolved to the IP address 192.xx.yy.zz, while the IP address pointed back to This mismatch resulted in the emails sent from the domain getting marked as spam.

Fixing Email Sending Problems

The basic problem with sending emails is that some other entity, a mail server, sends it on your domain’s behalf.

And guess what spammers do… They send emails on someone else’s behalf.

Sender Policy Framework – SPF

Sender Policy Framework (SPF) is an open standard specifying a technical method to prevent from address forgery in email messages. SPF allows the owner of a domain to specify which mail servers they use to send mail from that domain. Before diving further into SPF, it is first critical to understand that email messages actually have two different “From” addresses.

  1. The first is the return path address. It is a value that is also called the “envelope from” or “mail from”. The return path address informs receiving mail servers where to return, or bounce, a message back to if there is an error. The return path address is not displayed to the recipient.
  2. The second address is the one that is visible to recipients and is located in the headers of the email message. It is also called the “header from” address or the “friendly from” address. Since this is visible to recipients it is the only from address that most people are aware of in an email.

SPF specifically protects and authenticates the return path address used in the message delivery process.


Every major mailbox provider and anti-spam system have implemented SPF authentication checks, including:

  • Gmail/GoogleApps
  • Microsoft/Office365
  • Yahoo
  • AOL
  • Comcast
  • RoadRunner
  • Verizon


If you do not already have an SPF record for your domain:
1) Log in to the administrative area for your domain.
2) Locate the page from which you can update the DNS records.
3) Create a TXT record containing a text like this, depending on your mail server (e. g. authenticating Google Apps):

v=spf1 ~all

Adding another record would change the above example to:

v=spf1 ~all

This would allow both SocketLabs and Google Apps to transmit messages on-behalf of your domain.

Keep in mind that changes to DNS records may take up to 48 hours to propagate throughout the internet.


Adding a valid SPF record to your domain is a best practice, but is not enough to achieve a passing SPF alignment result for DMARC. By default, the “relaxed” alignment settings in DMARC require that the organizational domain used in both of the two “From” addresses are the same. That means if the domain you use in your from address in the message headers is [ ], then your return path address also needs to use an email address like [ ] or a subdomain such as [ ].

To check that you record is properly established and syntactically valid you can use any of the following third-party resources:

Kitterman SPF Verification Tool

Dmarcian SPF Survey Tool

DomainKeys Identified Mail (DKIM) Authentication

DomainKeys Identified Mail (DKIM) is a popular email authentication technology that allows for a domain to prove it is responsible for a message and that the message was not altered as it traveled the delivery path.

DKIM is a standard based on two previous authentication technologies, the DomainKeys standard from Yahoo and the Identified Internet Mail standard from Cisco. DKIM was formalized as a draft standard by the IETF in RFC 4781, published in May of 2007.

The basis of DKIM is that with the use of public keys published in the DNS records, messages can be authenticated in a non-path-related method. The authentication process revolves around the creation and decoding of what is called the DKIM signature. DKIM signatures are inserted into the header of an email message. A hash of the body and select header items is created and used in a calculation along with a private key value to create a message signature that can be decoded properly only with the public key which is posted in a domain’s DNS.

How To Improve WordPress Email Delivery

You might have had trouble with WordPress emails going into your spam folder. This is a common problem with emails that are sent from a website via PHP (the programming language that WordPress is based on).

Many spam filters, especially GMail, treat such emails with suspicion. This is with good reason. Servers can be set up to auto generate and send thousands of spam emails per hour.

The easiest way to fix the spam problem is to use an SMTP plugin. These plugins use the SMTP protocol to send email rather than the WordPress PHP email function.

SMTP (Simple Mail Transfer Protocol) is a mechanism you use to authenticate all outgoing emails to ensure that they are signed by the server before sending. By authenticating via SMTP, you are sending your emails from a real user account, and your emails will be less likely to be marked as spam. WordPress can send emails by SMTP with an authentication plugin that connects your site mail() function with a valid email server.

You will need an email provider. Such as the email that comes with your web hosting account a provider like Gmail. You’ll also need to find your SMTP server details and username and password.

WP Mail SMTP is an SMTP plugin. Just download it and activate. You’ll need to manually input your SMTP details.

Gmail SMTP: Gmail, the email service by Google, allows you to send out secure emails to your subscribers and customers directly from your site by authenticating via SMTP. The Gmail SMTP connects your website wp_mail function with Gmail securely through the OAuth 2.0 protocol. In this way, you do not need to save your SMTP password on your WP dashboard.

SocketLabs plugin: Each and every message that processes through the SocketLabs On-Demand Platform is automatically signed with a DKIM signature that authenticates as the point of origin for your messages. This allows every message processing on our platform to properly authenticate at the major service providers. No action is required for DKIM authentication to occur.

If you run a successful e commerce or membership site that sends out a lot of emails, you might need a email delivery service.

Email delivery services are designed to handle sending large volumes of transactional emails. These services do everything they can to ensure your emails avoid the spam folder. They are different from email newsletter services like MailChimp and AWeber.

What Are Spam Traps

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.

Content Tips To Avoid Spam Filters

Spam filters are 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.

Here are the things to take care of to avoid spam filters:

1. Pay Attention to Technical Matters

Keep the above technical issues surrounding the process of email marketing that you can take care of to maximize your email deliverability:

2. Use a recognizable sender name

It’s a good practice to always 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.

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. 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:

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

3. Choose a reliable Email Service Provider

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. Test each email before sending

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.

6. Keep your 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:

7. Never 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.

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!

8. 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.

9. Pay attention to 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 domain which directly influences deliverability rates. So, either launch a re-engagement campaign or unsubscribe those you don’t get a feedback from.

10. 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.

11. 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!

12. Respect 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.

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.

13. Take good care of subject lines

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.

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.

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.

15. 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.

16. 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 Joe, 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.

17. 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:

18. 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.

19. 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.

20. Tone down the fonts and colors

People seem to pay a lot of attention to the fonts and colors used in the copy. 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.

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!

21. 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:

22. 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.

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.

23. Make it easy to unsubscribe

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.

24. Take care of the follow-up

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.

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.

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.


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