Why are email blocks and bounces higher than normal and are bot unsubscribes happening?
Michael Ko
Co-founder & CEO, Suped
Published 18 Jun 2025
Updated 18 Aug 2025
6 min read
Suddenly seeing an uptick in email blocks, bounces, or even suspicious unsubscribes can be alarming. It directly impacts your ability to reach your audience and can signal deeper issues with your email program. When this happens, it's natural to wonder what's going on and if bots are playing a role.
I often hear from email senders facing these challenges, especially concerning unexpected surges in activity. There are many factors that can contribute to these issues, from technical misconfigurations to evolving mailbox provider policies or even automated threats.
Understanding email blocks and bounces
Email bounces occur when a message cannot be delivered to the recipient's server. These are broadly categorized into two types, each with different implications for your email list health and sender reputation. Understanding the distinction is crucial for effective troubleshooting.
Hard bounces are permanent delivery failures, often due to an invalid or non-existent email address. Sending to too many hard bounces can severely damage your sender reputation and lead to your IP address or domain being put on a blacklist (or blocklist). Mailbox providers like Gmail and Yahoo monitor these closely. If you're seeing a spike in Gmail hard bounces or Yahoo 'mailbox not found' rates, it indicates a need for immediate list cleaning.
Soft bounces are temporary delivery issues, such as a full inbox, server downtime, or a message that is too large. While less critical than hard bounces, a high volume of soft bounces can still affect your sender reputation, as they may indicate issues with recipient engagement or list quality. Repeated soft bounces to the same address might eventually be treated as a hard bounce by some systems.
Severe negative impact on sender reputation, leads to blocklisting. Remove immediately.
Soft bounce
Temporary delivery failure, e.g., mailbox full, server issues, message too large.
Minor impact initially, but recurring soft bounces can degrade sender reputation. Retries may occur.
Block
Recipient server actively rejects the email, often due to spam filters or blocklist entry.
Significant deliverability issues, can lead to widespread inboxing problems. Requires investigation.
Common causes for increased issues
Several factors can cause an unexpected rise in block (or blacklist) and bounce rates. One primary culprit is poor list hygiene. If your email list contains a significant number of inactive, misspelled, or non-existent addresses, you'll inevitably see higher hard bounce rates. Sending to spam traps can also trigger blocks.
Technical misconfigurations of email authentication protocols are another common reason. If your SPF, DKIM, or DMARC records are incorrectly set up, or if your domain is not properly authenticated, recipient servers might reject your emails, leading to blocks or bounces. This is especially true with the new Outlook and Gmail sender requirements.
Content-related issues can also contribute significantly. Messages that contain spammy keywords, suspicious links, or disproportionate image-to-text ratios can trigger spam filters, leading to blocks. A sudden increase in your sending volume, especially to an unengaged list, can also raise red flags with mailbox providers and result in higher bounce rates or even emails going to spam.
Common causes of blocks and bounces
Poor list quality: Sending to inactive, misspelled, or non-existent email addresses increases hard bounces. Regular list cleaning is essential.
Authentication failures: Missing or incorrect SPF, DKIM, or DMARC records can lead to emails being blocked by recipient servers.
Spammy content: Keywords, excessive links, or poor formatting can trigger spam filters. Content analysis helps identify problematic elements.
Sudden volume spikes: Abrupt increases in sending volume can raise suspicion with mailbox providers, leading to temporary blocks or throttling.
The rise of bot activity and its impact
Beyond blocks and bounces, an unsettling trend is the rise of bot activity impacting email metrics. This can manifest as inflated clicks or, more concerningly, unusual unsubscribes that appear to be automated. These bot unsubscribes often stem from security scanners or malicious bots that automatically click on links, including the one-click unsubscribe headers that Gmail and Yahoo now promote.
Identifying bot unsubscribes can be challenging, as they might mimic legitimate user behavior. However, patterns such as rapid, sequential unsubscribes from multiple users across different campaigns, without corresponding user-side activity (e.g., changes to newsletter preferences in your system), can be strong indicators. This inflated click activity can distort your engagement metrics and artificially deflate your list size, making it difficult to report accurate figures to internal teams like sales.
While some bot activity is harmless, others can be nefarious, attempting to degrade your sending reputation or even perform denial-of-service attacks on your email infrastructure by triggering mass complaints. Monitoring Google Postmaster Tools and your ESP's logs for unusual patterns is key to identifying and mitigating such threats before they cause significant damage.
Legitimate unsubscribes
User intent: Driven by the recipient's decision to no longer receive emails.
Pattern: Typically gradual, spread out, and may correlate with lack of engagement.
Impact: Healthy list cleansing, reduces spam complaints from disengaged users.
Bot unsubscribes
Automated action: Triggered by security scanners or malicious scripts.
Pattern: Often sudden, in rapid bursts, across multiple emails or a large portion of the list, without human interaction.
To effectively combat higher blocks, bounces, and bot activity, a proactive and systematic approach is essential. First, regularly monitor your deliverability metrics using your ESP's reports and external tools. Look for sudden spikes or declines that deviate from your baseline. Pay close attention to the specific bounce codes provided, as they offer clues about the underlying problem.
Second, maintain impeccable list hygiene. Implement a double opt-in process to ensure all subscribers genuinely want your emails. Regularly clean your list by removing hard bounces immediately and suppressing unengaged subscribers. This practice not only improves deliverability but also protects your domain reputation. Consider using a list validation service periodically to catch invalid addresses before sending.
Third, ensure your email authentication is solid. Proper implementation of SPF, DKIM, and DMARC is non-negotiable for modern email deliverability. DMARC, in particular, provides valuable feedback on how your emails are being treated and helps prevent spoofing. Regularly review your DMARC reports for authentication failures or unexpected rejections.
Segment and personalize: Send relevant content to engaged segments to boost positive interactions.
Views from the trenches
The email deliverability landscape is constantly evolving, with mailbox providers tightening their rules in response to spam and malicious activity. Sharing experiences helps the community navigate these challenges. Below are insights from peers regarding increased blocks, bounces, and bot unsubscribes.
Best practices
Actively monitor your bounce and block rates using granular reporting to spot anomalies quickly.
Implement double opt-in for all new subscribers to verify email addresses and prevent spam traps.
Regularly clean your email lists to remove inactive addresses and hard bounces, protecting your sender reputation.
Ensure SPF, DKIM, and DMARC records are correctly configured and aligned for strong email authentication.
Segment your audience and personalize content to improve engagement and reduce unsubscribes.
Common pitfalls
Ignoring bounce reports, leading to repeated sends to invalid addresses and a damaged sender reputation.
Not implementing DMARC or having it in monitoring mode (p=none) indefinitely, missing out on crucial feedback.
Sending to unengaged segments, which increases spam complaints and bounces over time.
Failing to monitor third-party blacklists or blocklists, missing critical indicators of deliverability issues.
Disregarding sudden increases in unsubscribe rates or clicks, attributing them solely to user behavior without investigating bot activity.
Expert tips
Leverage advanced analytics to detect unusual patterns in unsubscribe requests, such as high volume in short periods or from uncharacteristic IP ranges.
Regularly audit your email content for spam trigger words, broken links, or suspicious formatting that might flag spam filters.
Collaborate closely with your ESP to understand their specific policies and any network-wide issues affecting deliverability.
Consider implementing CAPTCHAs or other bot detection mechanisms on your signup forms to prevent malicious subscriptions.
Stay informed about new mailbox provider requirements and industry best practices to adapt your sending strategy proactively.
Marketer view
Marketer from Email Geeks says they have seen higher blocks and bounces across the board for the last month or so, affecting both soft and hard bounces.
2022-03-02 - Email Geeks
Expert view
Expert from Email Geeks says that while they haven't seen anything concerning among their customers that couldn't be attributed to their own behaviors, others have mentioned issues with Yahoo and Gmail.
2022-03-02 - Email Geeks
Maintaining email health in a changing landscape
Increased email blocks, bounces, and suspicious bot activity are not merely isolated incidents. They are critical indicators that require immediate attention to maintain your sender reputation and ensure your messages reach the inbox. By understanding the causes and implementing best practices, you can mitigate these issues effectively.
Proactive monitoring, rigorous list hygiene, strong email authentication, and careful analysis of unusual engagement patterns are the pillars of a resilient email program. Staying vigilant and adaptable to the evolving email landscape is key to successful deliverability in the long run.
