Why are my marketing emails being blocked by the recipient?
Michael Ko
Co-founder & CEO, Suped
Published 13 Aug 2025
Updated 16 Aug 2025
6 min read
It is incredibly frustrating when you dedicate time and resources to crafting the perfect marketing email, only for it to be blocked by the recipient. You might spend hours on design, compelling copy, and audience segmentation, yet your message never even reaches the inbox. This issue is more common than many marketers realize and can significantly impact your campaign's effectiveness and ROI.
Email blocking isn't just about landing in the spam folder, though that's a common symptom. Sometimes, recipient servers outright reject your emails, preventing them from being delivered at all. This can happen silently, leaving you wondering why your engagement rates are plummeting.
Understanding the root causes of these blocks is the first step towards ensuring your marketing messages consistently reach their intended audience. We'll explore the primary reasons why your emails might be getting blocked and provide actionable strategies to fix these deliverability issues.
Sender reputation and blacklists
At the heart of email deliverability lies your sender reputation. ISPs (Internet Service Providers) like Google and Microsoft continuously evaluate your sending practices. A positive reputation indicates you're a trustworthy sender, while a poor one flags your emails as potential spam, leading to blocks.
One of the most immediate threats to your deliverability is being listed on an email blacklist (also known as a blocklist). These lists, maintained by various organizations, identify IP addresses and domains associated with sending unwanted mail. If your sending infrastructure ends up on one of these, it's a near certainty your emails will be blocked. You can learn more about what happens when your domain is on an email blacklist.
Factors that contribute to a damaged sender reputation and potential blocklist inclusion include high spam complaint rates, consistently high bounce rates (especially hard bounces), and hitting spam traps. These signals tell ISPs that your mailing practices are problematic, making them wary of accepting your emails. Understanding how your email address ends up on a blacklist is crucial for prevention.
Authentication failures
Email authentication protocols are foundational for proving your legitimacy. SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) work together to verify that an email truly originates from the domain it claims to be from. For a simple overview, see a simple guide to DMARC, SPF, and DKIM.
Failures in these authentication checks are increasingly a primary reason for email blocks. With new, stricter sender requirements from major mailbox providers, unauthenticated emails are often rejected outright. Even minor misconfigurations can lead to significant delivery problems, as receiving servers cannot reliably confirm the sender's identity.
Proper DMARC implementation is especially critical. A DMARC policy set to "reject" (p=reject) will instruct recipient servers to block emails that fail authentication. While this is the strongest protection against spoofing, if your legitimate emails aren't correctly authenticated, they will also be rejected. Regular DMARC monitoring is essential to catch these issues.
Common authentication errors
SPF PermError: Exceeding the 10 DNS lookup limit in your SPF record, often due to including too many third-party sending services.
DKIM Invalid Signature: The email content was altered in transit, or the DKIM record is incorrectly published or expired.
DMARC Alignment Failure: The 'From' address domain doesn't align with the SPF or DKIM authenticated domain, causing the DMARC check to fail.
Content and recipient engagement
Beyond technical configurations, the actual content of your marketing emails plays a significant role in deliverability. Spam filters analyze various elements within your email, and certain patterns or practices can trigger them, causing your emails to be blocked or routed to the spam folder. These include excessive use of spammy keywords, broken HTML, or too many images relative to text.
Recipient engagement is another critical signal to ISPs. If subscribers consistently ignore, delete, or, worse, mark your emails as spam, it tells the ISP that your content isn't desired. Low open rates, low click-through rates, and high unsubscribe rates all contribute to a negative engagement score, making your emails more likely to be blocked. Read Kinsta's insights on why emails go to spam for more.
The quality of your email list is paramount. Sending to invalid, old, or unengaged email addresses leads to high bounce rates and can even cause you to hit spam traps. These actions severely damage your sender reputation and increase the likelihood of blocks. Always ensure you have explicit permission to email your subscribers and regularly clean your lists to remove problematic addresses.
Best content practices
Personalized content: Tailor messages to individual interests and behaviors.
Clear calls to action: Make it easy for recipients to engage.
Clean HTML: Use well-structured and concise code.
Relevant subject lines: Accurately reflect email content without being misleading.
Content red flags
Keyword stuffing: Overusing trigger words associated with spam.
Deceptive subject lines: Misleading recipients about the email's purpose.
Bought lists: These often contain spam traps and unengaged users.
Infrastructure and administrative hurdles
Sometimes, the problem isn't your sending practices but rather the recipient's email infrastructure or internal policies. Corporate networks, for instance, often employ stringent email security measures, including firewalls and advanced spam filters, which can block even legitimate marketing emails. This is a common challenge, especially when dealing with deliverability issues with Microsoft Outlook and Hotmail.
Your choice of IP address, whether shared or dedicated, also plays a role. If you use a shared IP address, your deliverability can be affected by the sending behavior of other users on that same IP. If one bad sender gets the IP blocklisted (or blacklisted), all senders on that IP suffer. High-volume senders often benefit from dedicated IPs to maintain better control over their sending reputation.
Internal IT teams and mail administrators within organizations can implement specific rules that block emails from certain domains or IPs. If your marketing emails are consistently blocked by a particular company, their IT department might have set up a custom block. In such cases, direct communication or requesting whitelisting might be necessary. Tools like Microsoft 365 Defender's advanced hunting can help identify why emails are being quarantined.
Monitor DMARC reports closely for authentication failures and adjust policies as needed.
Maintain a clean and engaged email list by regularly removing inactive subscribers.
Proactively check for blocklist listings using reputable monitoring services.
Ensure all email authentication records (SPF, DKIM, DMARC) are correctly configured.
Common pitfalls
Ignoring DMARC p=none reports, which can hide underlying authentication problems.
Sending to unverified or old email addresses, leading to high bounce rates.
Failing to warm up new IPs or domains before sending large volumes of emails.
Whitelisting an entire ESP, which can expose your domain to risks from other senders.
Expert tips
Consult your internal IT team for corporate-level blocking issues, as they can check logs.
Utilize advanced hunting features in email security platforms to diagnose delivery issues.
Never migrate email providers during peak sending periods, as it can cause disruptions.
Ensure your ESP can provide specific IP addresses for whitelisting if needed by recipient IT.
Marketer view
Marketer from Email Geeks says: We encountered hard bounces and immediate suppression during an email platform migration, which caused significant issues with our marketing communications.
2022-11-30 - Email Geeks
Expert view
Expert from Email Geeks says: Emails are likely being blocked by internal IT rules, and the IT team will need to whitelist the specific sending service.
2022-11-30 - Email Geeks
Ensuring your marketing emails land in the inbox
Ensuring your marketing emails reach the inbox is a multifaceted challenge that requires ongoing vigilance. From maintaining a stellar sender reputation and implementing robust authentication to crafting engaging content and navigating recipient-side filters, every element contributes to your deliverability success.
By proactively addressing these common issues and continuously monitoring your email performance, you can significantly reduce the likelihood of your marketing emails being blocked. Consistent effort in these areas will lead to improved inbox placement and, ultimately, more effective marketing campaigns.
Google and 
Microsoft continuously evaluate your sending practices. A positive reputation indicates you're a trustworthy sender, while a poor one flags your emails as potential spam, leading to blocks.
