What steps should I take when my email campaign experiences block bounces?
Michael Ko
Co-founder & CEO, Suped
Published 1 Aug 2025
Updated 16 Aug 2025
9 min read
Experiencing block bounces in your email campaign can be incredibly frustrating. One moment your emails are delivering, the next, a significant portion are bouncing back, undelivered. This is a common, though unwelcome, issue that many email marketers face. Block bounces typically indicate that the receiving mail server has actively rejected your message, often due to perceived spam, low sender reputation, or being listed on a blacklist (or blocklist).
The immediate impact is clear: your messages aren't reaching their intended audience, which can severely disrupt communication, marketing efforts, and sales. Beyond the immediate non-delivery, a high rate of block bounces can also signal deeper issues with your sending practices, potentially damaging your sender reputation over time. This makes it harder for future emails to reach the inbox, even for legitimate communications.
The good news is that block bounces are often solvable. Addressing them requires a systematic approach, starting with diagnosis and moving towards strategic adjustments and ongoing monitoring. Understanding why you're being blocked is the first crucial step to getting your email campaigns back on track and ensuring your messages land in the inbox.
Identifying the cause of block bounces
When block bounces occur, the very first step is to pause and investigate. Continuing to send emails without understanding the problem can worsen your situation, leading to further reputation damage or even permanent blacklisting. Your email service provider (ESP) should provide detailed bounce reports or logs. These reports contain crucial bounce messages that offer clues about why your emails are being rejected. Look for specific error codes or descriptive text from the receiving servers.
Pay close attention to whether the bounces are originating from specific domains or mailbox providers, such as Gmail, Microsoft (Outlook/Hotmail), or Yahoo/AOL. This can narrow down the potential cause. For instance, if bounces are predominantly from Yahoo, it might indicate specific Yahoo-related deliverability issues rather than a general problem. You can often find common SMTP bounce codes and their meanings, which help decipher the issue.
A common reason for block bounces is your IP address or domain being listed on an email blacklist (or blocklist). These are databases of IP addresses and domains known to send spam or malicious emails. Many mailbox providers use these lists to filter incoming mail. You can use a blocklist checker to see if you are listed. If you find your IP or domain on a blocklist, the bounce messages often explicitly state which one. If your new IP address is blocked on its first send, this requires specific troubleshooting steps. It's crucial to understand what happens when your domain is blacklisted and how blocklists function.
Understanding the precise nature of the block bounce is key. Is it a temporary soft bounce, like a "server too busy" error, or a permanent hard bounce? Hard bounces, such as "user unknown", require immediate removal from your list. Soft bounces might resolve themselves, but repeated soft bounces can also hurt your reputation and lead to blocklisting. This initial diagnostic phase is critical for developing an effective recovery plan.
Addressing the root issues affecting deliverability
Once you've identified the specific reasons for your block bounces, it's time to address the underlying issues. Often, the problem stems from your sender reputation, which is influenced by factors like email authentication, content quality, and list hygiene. Ensuring proper email authentication, including SPF, DKIM, and DMARC, is fundamental. Misconfigurations in these records can lead to emails being flagged as suspicious or spoofed, resulting in blocks. For example, a fixed SPF failure might not immediately resolve blockages from Gmail and Microsoft without further action.
Email content plays a significant role in deliverability. Using spammy keywords, excessive images, broken links, or an imbalanced text-to-image ratio can trigger spam filters and lead to blocks. Regularly review your email content for anything that might appear suspicious. Also, consider the engagement of your subscribers. Sending to an unengaged list with a high bounce rate signals to mailbox providers that your emails might not be wanted. This can lead to a damaged sender reputation and increased blockages.
List hygiene is arguably one of the most critical factors. High hard bounce rates, spam trap hits, and sending to inactive mailboxes are major red flags that can get your IP or domain blacklisted. Regularly cleaning your email list to remove invalid, inactive, or unengaged addresses is paramount. This includes promptly removing hard bounced email addresses and managing soft bounces effectively. Think of it this way, a clean list contributes to a healthy sender reputation, which in turn improves deliverability.
Common causes of block bounces
IP/Domain blacklist: Your sending IP or domain is listed on a spam blacklist, used by ISPs to block known spammers.
Poor sender reputation: Low engagement, high complaints, or frequent spam trap hits degrade your reputation, leading to blocks.
Invalid email addresses: Sending to a high percentage of non-existent emails results in hard bounces and signals poor list quality.
Content issues: Spammy subject lines, suspicious links, or certain attachments can trigger spam filters.
Authentication failures: Incorrect or missing SPF, DKIM, or DMARC records can cause mail servers to reject your emails.
Strategies for unblocking and preventing future issues
Once you understand the cause of the block bounces and have begun to address the underlying issues, the next step is often to request removal from the specific blocklist (or blacklist) that has listed your IP or domain. Most blocklists provide a delisting process, usually through a form on their website. When submitting a delisting request, be honest about the issue and explain the steps you've taken to resolve it. Some blocklists, like Proofpoint, might even have an automated process that can unblock your IP quickly. However, relying on repeated self-unblocks without fixing the core problem is not a sustainable strategy and can lead to more severe, permanent blockages.
After delisting, you need to implement proactive measures to prevent future block bounces. This includes continuous monitoring of your sender reputation and bounce rates. Monitor your blocklist monitoring to ensure you are not relisted. Regularly checking your DMARC reports can also provide early warnings of authentication issues that could lead to blocks. These tools provide visibility into your email performance and help you catch potential issues before they escalate.
Engage with your email service provider's (ESP) deliverability team. They have deep insights into industry trends, common issues, and specific blocklist requirements. They can often provide tailored advice and help you troubleshoot complex problems that might not be immediately apparent from bounce codes alone. Leaning on their expertise can significantly expedite the recovery process and help you refine your sending practices. For example, some ESPs have specific advice for managing bounce mail within their platform.
Maintaining an excellent sender reputation is an ongoing effort. It involves consistently sending relevant content, managing subscriber expectations, and adhering to email best practices. This proactive approach not only helps resolve current block bounces but also builds resilience against future deliverability challenges, ensuring your email campaigns remain effective.
Navigating and learning from block bounces
When facing email campaign block bounces, a common pitfall is to panic and immediately resend without understanding the problem. This can often exacerbate the issue, leading to further blocks or a worsened sender reputation. Instead, the focus should be on thorough investigation and a systematic approach to identify and rectify the root causes. Often, the bounces aren't just random occurrences, but indicators of underlying issues like poor list hygiene or authentication problems.
Understanding the specific bounce messages is crucial. These messages contain error codes and descriptions that pinpoint why your emails are being rejected. Neglecting to read these details is like trying to fix a car without knowing what's wrong with it. Knowing the exact error, whether it's a "server too busy" soft bounce or a permanent block due to a blacklist, guides your next steps. Many times, the issue is not unique to your situation, and your ESP or community forums can offer insights.
Finally, remember that resolving block bounces is an iterative process. It requires diligence in monitoring, adapting your sending strategies, and maintaining rigorous list hygiene. A proactive approach, combined with a willingness to delve into the technical details of email deliverability, will set you up for long-term success.
Views from the trenches
Best practices
Always halt sending immediately after detecting a high rate of block bounces to prevent further reputation damage.
Thoroughly analyze bounce messages and logs to understand the exact nature and origin of the rejections.
Check relevant email blocklists (blacklists) to see if your IP or domain is listed and understand the specific reasons for the listing.
Actively maintain and clean your email lists to remove invalid, inactive, and unengaged addresses, minimizing hard bounces and spam trap hits.
Regularly review your email content for spam trigger words, suspicious links, and proper formatting to avoid spam filters.
Common pitfalls
Continuing to send emails without investigating block bounces, which can worsen your sender reputation and lead to permanent blocks.
Ignoring bounce messages and not understanding the specific error codes, preventing effective troubleshooting.
Attempting repeated self-unblocks from blocklists without addressing the underlying issues, leading to more severe blockages.
Failing to implement proper email authentication (SPF, DKIM, DMARC), which is crucial for establishing sender legitimacy.
Not engaging with your email service provider's deliverability team for expert guidance and support when issues arise.
Expert tips
Proactively monitor your sender reputation metrics, including complaint rates, spam trap hits, and engagement, to detect issues early.
Implement a double opt-in process for new subscribers to ensure high-quality and engaged contacts, reducing future bounce risks.
Segment your email lists based on engagement and sending frequency to tailor content and minimize sending to unengaged recipients.
Regularly test your email deliverability using an email deliverability tester before large campaigns to identify potential issues.
Stay updated on major mailbox provider requirements and industry best practices to adapt your strategies accordingly.
Expert view
Expert from Email Geeks says to immediately stop sending and investigate where the blocks are occurring, as well as audit how the email list was acquired.
2023-04-01 - Email Geeks
Marketer view
Marketer from Email Geeks says not to panic and to check the bounce errors, as it might be a simple mistake that can be fixed quickly.
2023-04-01 - Email Geeks
Maintaining a healthy sending reputation
Dealing with block bounces can be a stressful experience, but it's also an opportunity to strengthen your email program. By systematically investigating the bounce messages, identifying the underlying causes, and implementing a robust strategy, you can overcome these hurdles.
Remember, a healthy sender reputation is built on consistent best practices, including meticulous list hygiene, engaging content, and proper email authentication. Proactive monitoring and a willingness to adapt are your strongest tools against future blockages and deliverability issues.
By taking these steps, you not only resolve immediate block bounces but also lay the groundwork for long-term email marketing success, ensuring your messages consistently reach the inboxes they're intended for.
Gmail, 
Microsoft (Outlook/Hotmail), or 
Yahoo/AOL. This can narrow down the potential cause. For instance, if bounces are predominantly from Yahoo, it might indicate specific Yahoo-related deliverability issues rather than a general problem. You can often find common SMTP bounce codes and their meanings, which help decipher the issue.
