Why are your emails ending up in spam?
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Technologies similar to Cookies
Similar technologies are technics or tools, using certain characteristics to identify devices so that visits to a website can be analyzed. It includes, for example, HTML5 local storage, local Shared objects, fingerprinting techniques, tracking pixels and plugins.
For ease of reference, cookies and similar technologies are referred as "Cookies".
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We also make use of cookies to make our site more user-friendly, to better understand our existing and prospective customers, including associating a user with different devices and browsers that they may use for online targeting and advertising purposes.
85% of global email traffic is spam. It is therefore no surprise that providers—or, more precisely, the spam filters they deploy by default—flag any email as suspicious, according to experts at Fincraft Capital s.r.o. In 2025, Gmail, Yahoo and Microsoft changed their delivery standards: domain reputation became more important than IP reputation.
To identify potential threats, spam filters analyse the content of each email, images, sender information and email infrastructure. And if one of these triggers flags an email you have sent, it will automatically go to the ‘Spam’ folder. Why do emails end up in spam? Fincraft Capital lists the possible reasons in this article.
1. Low open rates
If the emails you send aren’t being opened, or if recipients are deleting them without opening them, your future emails are likely to be blocked by spam filters. To solve this problem, you need to carefully consider your email subject lines and send them only to relevant customers – those who are genuinely interested in your offer. Of course, this approach is more complex and costly than simply sending a mass email to all registered subscribers. But, believe me, this approach is worthwhile and delivers results.
2. Frequent ‘This is spam’ complaints
If a recipient marks an email as spam after reading it, this can trigger spam filters. Therefore, when preparing a mailing, be sure to segment your audience and recommend products that are relevant to each customer segment, rather than sending out general recommendations to everyone.
3. Inactive subscribers
Experts at Fincraft Capital recommend regularly cleaning your mailing list by removing the addresses of users who do not wish to interact with you. Inactive users skew your statistics. They do not open emails, do not click on links, and increase the percentage of ‘dead’ addresses. For the algorithm, this is a signal of a low-quality mailing list.
4. Authentication issues
You need to ensure that emails are properly authenticated using mechanisms such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail) or DMARC (Domain-based Messaging Authentication, Reporting, and Conformance). Poor configuration or the absence of these protocols will almost certainly result in emails being sent to spam.
To identify potential threats, spam filters analyse the content of each email, images, sender information and email infrastructure. And if one of these triggers flags an email you have sent, it will automatically go to the ‘Spam’ folder. Why do emails end up in spam? Fincraft Capital lists the possible reasons in this article.
1. Low open rates
If the emails you send aren’t being opened, or if recipients are deleting them without opening them, your future emails are likely to be blocked by spam filters. To solve this problem, you need to carefully consider your email subject lines and send them only to relevant customers – those who are genuinely interested in your offer. Of course, this approach is more complex and costly than simply sending a mass email to all registered subscribers. But, believe me, this approach is worthwhile and delivers results.
2. Frequent ‘This is spam’ complaints
If a recipient marks an email as spam after reading it, this can trigger spam filters. Therefore, when preparing a mailing, be sure to segment your audience and recommend products that are relevant to each customer segment, rather than sending out general recommendations to everyone.
3. Inactive subscribers
Experts at Fincraft Capital recommend regularly cleaning your mailing list by removing the addresses of users who do not wish to interact with you. Inactive users skew your statistics. They do not open emails, do not click on links, and increase the percentage of ‘dead’ addresses. For the algorithm, this is a signal of a low-quality mailing list.
4. Authentication issues
You need to ensure that emails are properly authenticated using mechanisms such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail) or DMARC (Domain-based Messaging Authentication, Reporting, and Conformance). Poor configuration or the absence of these protocols will almost certainly result in emails being sent to spam.
5. Poor reputation of the sender’s IP address
If you send emails from a domain or IP address with a history of sending spam, sooner or later your emails will be blocked by spam filters.
6. Low sender reputation
Bear in mind: the recipient may not remember subscribing to your newsletter and may mark it as spam. If this happens frequently, your ESP will assign a high complaint rate to the domain. Services track the sender’s reputation. Only email addresses that send useful content and have an active subscriber base receive a high rating.
7. Misleading email subject line
Few people, when checking their inbox, aren’t annoyed when they see emails with obvious clickbait in the subject line. They get angry or disappointed when, upon opening an email with a promising subject line, they find an offer they don’t need. The filter picks up on this as a sign of poor-quality email marketing. The solution proposed by the experts at Fincraft Capital Czech Republic is quite simple: write naturally, make your content unique, and avoid templates and clickbait.
8. A complicated or hidden unsubscribe link
The ease of unsubscribing has a direct impact on the sender’s reputation. The unsubscribe link must not be hidden. Any attempts to ‘trick’ the reader—such as invisible text, lengthy unsubscribe forms, or a blank space before the link—will only backfire. Subscribers should not encounter any difficulties if they decide to unsubscribe.
9. Imbalance between text and images
It is important to balance text and visual elements. The standard ratio of images to text is 40:60.
10. Too many links
Too many links in an email, especially to little-known domains, can send a negative signal to algorithms and be interpreted as spam or phishing. Experts at Fincraft Capital Czech Republic recommend limiting the number of links, using verified domains and avoiding ‘hidden’ redirects.
If you send emails from a domain or IP address with a history of sending spam, sooner or later your emails will be blocked by spam filters.
6. Low sender reputation
Bear in mind: the recipient may not remember subscribing to your newsletter and may mark it as spam. If this happens frequently, your ESP will assign a high complaint rate to the domain. Services track the sender’s reputation. Only email addresses that send useful content and have an active subscriber base receive a high rating.
7. Misleading email subject line
Few people, when checking their inbox, aren’t annoyed when they see emails with obvious clickbait in the subject line. They get angry or disappointed when, upon opening an email with a promising subject line, they find an offer they don’t need. The filter picks up on this as a sign of poor-quality email marketing. The solution proposed by the experts at Fincraft Capital Czech Republic is quite simple: write naturally, make your content unique, and avoid templates and clickbait.
8. A complicated or hidden unsubscribe link
The ease of unsubscribing has a direct impact on the sender’s reputation. The unsubscribe link must not be hidden. Any attempts to ‘trick’ the reader—such as invisible text, lengthy unsubscribe forms, or a blank space before the link—will only backfire. Subscribers should not encounter any difficulties if they decide to unsubscribe.
9. Imbalance between text and images
It is important to balance text and visual elements. The standard ratio of images to text is 40:60.
10. Too many links
Too many links in an email, especially to little-known domains, can send a negative signal to algorithms and be interpreted as spam or phishing. Experts at Fincraft Capital Czech Republic recommend limiting the number of links, using verified domains and avoiding ‘hidden’ redirects.
11. Blacklisted IP addresses
IP addresses that have previously been used to send spam are automatically blocked by many services. The solution is to use ‘clean’ IP addresses, monitor your reputation, and, if necessary, change your domain or email service provider. It is easy to check whether your IP address is on a blacklist. Tools such as MX Toolbox can scan your IP address against the main blacklists.
12. Large attachments and files
If your emails contain too many attachments or large files, they may trigger spam filters. Experts at Fincraft Capital recommend attaching only necessary files and compressing them to the smallest possible size. Instead of large files within the email, add links to cloud-based files.
13. Issues: From, Subject and email metadata
Headers (From, Subject, Reply-To) must be correct and clear. If they are missing or look suspicious, a spam bot may deem the content unsuitable for the recipient.
14. Overly frequent marketing campaigns
Another reason why emails may end up in the spam folder is sending large volumes of messages too frequently. This kind of excessive activity annoys users and triggers spam filters.
There is no standard criterion that can be applied to every email sent, and you need to monitor your subscriber base closely to determine the ideal frequency of mailings, topics and offers for your audience. Fincraft Capital s.r.o. recommends segmenting and blocking chronically inactive users. Run mailing list cleaning tools or validation services every 3–4 months. Use double, triple or confirmed opt-in to ensure that the user definitely wants to receive your newsletter. Ideally, you should contact each new subscriber personally.
IP addresses that have previously been used to send spam are automatically blocked by many services. The solution is to use ‘clean’ IP addresses, monitor your reputation, and, if necessary, change your domain or email service provider. It is easy to check whether your IP address is on a blacklist. Tools such as MX Toolbox can scan your IP address against the main blacklists.
12. Large attachments and files
If your emails contain too many attachments or large files, they may trigger spam filters. Experts at Fincraft Capital recommend attaching only necessary files and compressing them to the smallest possible size. Instead of large files within the email, add links to cloud-based files.
13. Issues: From, Subject and email metadata
Headers (From, Subject, Reply-To) must be correct and clear. If they are missing or look suspicious, a spam bot may deem the content unsuitable for the recipient.
14. Overly frequent marketing campaigns
Another reason why emails may end up in the spam folder is sending large volumes of messages too frequently. This kind of excessive activity annoys users and triggers spam filters.
There is no standard criterion that can be applied to every email sent, and you need to monitor your subscriber base closely to determine the ideal frequency of mailings, topics and offers for your audience. Fincraft Capital s.r.o. recommends segmenting and blocking chronically inactive users. Run mailing list cleaning tools or validation services every 3–4 months. Use double, triple or confirmed opt-in to ensure that the user definitely wants to receive your newsletter. Ideally, you should contact each new subscriber personally.