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Why Your Emails May End Up in the Spam Box & How to Protect Your Emails from Spam Filter?

Spam is classified as irrelevant or unwanted emails that are sent in bulk to an email list. For example; Company “A” purchases an email list from a third-party source and starts sending their unsolicited business emails in bulk to the receivers on the list.  Company “A” sends these emails without having any clear idea of what the receivers in the list desire from a product or brand. Since those contacts in the list did not directly provide permission to Company “A” for marketing or promotional purposes, sending email messages to those contacts will lead to spam reporting. This is the primary reason why you may not recognize the communications you receive that have automatically ended up in your current spam folder. 

A Little Insight Into Spam Filters

Each spam filter functions differently. What constitutes  “passing” scores may vary from one spam filter to another filter. That’s why if an email passes through Spam Filter A without raising any issue may get flagged by when passing through Spam Filter B. Spam filters also sync with one another to share the sender’s insights and what they have learned about every sender. Hence, it is crucial to understand how spam filters work and how you can avoid getting redirected to subscribers’ spam folders.

Campaign Metadata

Spam filters collect information on whether the sender is familiar with the recipient who is receiving the email. That’s why use Tokens on Marketo to personalize your “To:” and “From” fields and send your emails through verified domains. You can also request your recipients to incorporate you as a sender in their address books.

Your IP address

Many spam filters flag an email marketing campaign when anyone with a similar IP address has sent any spam email earlier. Hence, if one person sends a spam email through a server, it can damage the email deliverability for other senders. That’s why you need to focus on maintaining your sender’s reputation score.

Coding, content, and formatting

Spam filters are triggered by code extracted from a Microsoft Word document, poorly written codes, or too many tags that may lead your emails flagged by spam filters. While some spam filters may also flag your emails based on their specific parameters of content, text, or images in emails. You can outsource your email design, email copy, and email campaign development tasks to specialists outside your inhouse team for specific projects to avoid the hassle of replacing and hiring new team members.  

How to Avoid Emails getting to Spam?

Ask subscribers to whitelist emails.

When you send welcome emails after signing up for your newsletter, ask your new subscribers to whitelist your emails. This is an easy way to improve your email deliverability and prevent your emails from getting landed in spam boxes instead of inboxes. Subscribers who have signed up also wish to receive your emails, so they are likely to whitelist your email address when asked. The more subscribers whitelist your emails, the more you can protect your sender’s reputation and ensure inbox delivery. 

Do not buy or rent email lists.

Third-party and cold leads are often against the rules in many countries. Contacts collected by purchasing or renting an email list also contain the risk of wrong or invalid addresses, which will only lead to high email bounce rates, more flagging, and blacklisting. Sending emails to these contacts who have not expressed any interest or given you permission can potentially damage your brand image and cause your legal hassles. Therefore, you should always practice growing your email list organically.

Single opt-in or double opt-in – what’s right for you? 

There are two effective methods of signup that are single opt-in and double opt-in. Both approaches have their own merits and demerits. While the double opt-in process requires subscribers to confirm their registration with the list can ensure their interests in your emails. Thus, subscribers obtained through this method will result in a few spam reports. However, many users may forget or skip performing the second step of confirmation. On the other hand, a single opt-in process involves a single and more straightforward measure of the signup process; many subscribers start marking emails as spam the moment they lose interest, or they feel they may have made a mistake when accepting your email signup request. Hence, you need to choose based on what’s best for your target audience. 

Add a signup form to hunt permission.

Do not send promotional emails without getting permission first. Consider adding a signup form to your website or giving customers a choice to check-in for your list once they make a purchase or inquiry from your site.

Use email preference centers. 

If your subscribers sign up for your monthly newsletters or biweekly newsletters – then comply with email frequency preferences and not send them weekly promotional emails. Eventually, they may start opening, engaging, or even responding to your emails. On the other hand, they may mark your emails as spam. To avoid this refer to the section above. Set up one email preference center in Marketo. There you can direct subscribers to select their preferred choice of email frequency, specific days of the week, or time of the day and choose topics they are interested in. 

Subscribers generated with email preference centers and following their preferences will stay longer and build faith in your brand. Thus, you can avoid the risk of spam reports and improve email delivery. 

Incorporate a link to unsubscribe from the email list 

Do not hide the unsubscribe/opt-out link in your campaigns. The CAN-SPAM Act requires adding an unsubscribe link in every email campaign you send. When an unsubscribe link is visible in emails, people who may no longer wish to receive your emails can unsubscribe from your list, and they will immediately be removed from your list. Often the ease of unsubscribing from your plan may encourage people to return to subscribe again. Additionally, you can avoid sending emails to people who are not interested and hence, not opening your emails, and they will not report your emails as spam. On the other hand, when people cannot find that the link in your emails, they will simply mark your message as spam.

Spam Filter Testing and Spam Checkers

Consider these spam checkers to scan your emails for issues.


Litmus is a suite that provides several email optimization tools, including a spam checker. Here’s how Litmus can help you prevent your emails being marked as spam:

  • It scans all your emails by every primary spam filter before sending so that they will pass the spam filter score.
  • It scans your sender’s reputation score by checking your IP addresses and domain names used in your emails and against every known blacklist. 
  • It checks if your email authentication such as SenderID, DomainKeys, DKIM, and Sender Policy Framework is set up correctly.
  • It also assigns you a spam score to suggest to you why you have got that score and how you can improve it.

Free Litmus-alternative spam checking tools

There are several free Litmus-alternative spam checking tools such as Mail-Tester and These free spam checking tools will also tell you if your emails will be blacklisted and give you spam ratings on a scale of 1 to 10. However, you have to check every email through these free spam checkers manually and lack a comprehensive email testing capability. However, it can check your SenderID, Sender Policy Framework, and DKIM to ensure they are set up in ways that will dodge spam filters without any issues. 


Do you find these tips on avoiding spam filters useful? Do you need professional assistance in spam-proof your email marketing campaign? Get your best results in email delivery and the sender’s reputation by consulting with our certified marketing operations experts. You can simply start chatting with us, using the chatbots below, or say “Hello” at If you want to reach us via social media, then you can simply DM us on Facebook, LinkedIn, and Twitter