Summary
When you introduce a new sending address or a new segment of recipients, especially from an acquisition, it can significantly impact your email deliverability. The sudden increase in bounce rates, both soft and hard, often indicates underlying issues related to sender reputation, list hygiene, and domain authentication. Understanding the specific bounce messages, such as "envelope blocked - User Entry - mimecast SMTP error code 550" and "rejected by header based manually blocked senders," is crucial, as these are strong indicators of explicit recipient blocks, not temporary issues.
Key findings
- Hard bounces defined: Messages like "envelope blocked - User Entry" or "rejected by header based manually blocked senders" are hard bounces, indicating permanent delivery failure because the recipient has explicitly blocked your sender. These are not soft bounces and should be treated as permanent failures.
- Impact of new sender addresses: Introducing a new sender address for a new, unengaged segment can immediately trigger blockages and reputation issues, even affecting your established sending addresses if the underlying sender domain or IP is shared.
- Recipient action: These bounce messages mean recipients actively do not want your mail, suggesting they may have previously attempted to unsubscribe or marked your emails as spam.
- Shared envelope domain risk: If your sending envelope address (return-path domain) is shared with other senders, their poor sending practices or recipient blocks can negatively impact your overall deliverability, even for your existing, well-behaved segments.
- List hygiene importance: Acquired lists often contain outdated, invalid, or unengaged contacts, which can lead to high bounce rates and spam trap hits, severely damaging sender reputation.
Key considerations
- Immediate removal: Any email address generating a hard bounce (especially user-entry blocks) should be immediately removed from your active mailing lists. Continuing to send to these addresses will only exacerbate reputation issues.
- Sender address strategy: While changing the sender address might offer a temporary reprieve, it is not a sustainable solution if the underlying issue is recipient disengagement or explicit blocking.
- Investigate unsubscribe history: Reviewing the history of blocked addresses for previous unsubscribe attempts or engagement issues can provide valuable insights into why recipients are blocking your mail.
- Dedicated envelope domains: Consider if your email service provider (ESP) allows for a custom envelope domain (return-path domain) solely for your sending. This can help isolate your sender reputation from other users on a shared domain.
- Sender reputation repair: Focus on improving your sender reputation by adhering to email deliverability best practices, which includes list cleaning, segmenting, and proper authentication (SPF, DKIM, DMARC).
What email marketers say
Email marketers often face challenges when integrating new contact lists or changing sender addresses, as these actions can unexpectedly trigger high bounce rates. Their experiences highlight the importance of careful list management and understanding how recipient behavior directly impacts deliverability. Many marketers express concern about maintaining sender reputation and avoiding blacklists (or blocklists) when expanding their outreach or changing sending parameters.
Key opinions
- New segment risks: Sending to a newly acquired or never-emailed segment, especially with an unfamiliar sender address, is frequently cited as a direct cause of immediate deliverability issues and increased bounces.
- Impact on existing lists: Marketers observe that problems originating from new segments or sender addresses can spill over and negatively affect deliverability for their established, active contact lists.
- Recognizing explicit blocks: Bounce messages indicating 'user entry' blocks are understood as clear signals that the recipient has manually added the sender to their blocked list, which is a severe form of hard bounce.
- Sender address changes: There's a common belief that changing the sender address might temporarily bypass recipient blocks, but this is viewed as a short-term fix that doesn't address the core problem.
- Platform capabilities: Some marketers are exploring or are aware of their ESP's capabilities, such as Eloqua, to configure custom envelope addresses to better manage their sending reputation.
Key considerations
- List hygiene best practices: Regularly cleaning email lists and removing unengaged or invalid contacts is paramount to reducing bounce rates and maintaining good deliverability. This includes understanding the definitions of soft and hard bounces to manage your list effectively.
- Sender reputation management: Marketers must proactively monitor their sender reputation and take steps to repair it when issues arise, such as a high bounce rate. You can learn more about how long it takes to recover domain reputation.
- Avoiding blocklists: Ignoring high bounce rates or continuing to send to blocked addresses can lead to getting listed on email blocklists, severely hindering future email campaigns. Our in-depth guide to email blocklists provides further detail.
- Understanding bounce types: It's important for marketers to differentiate between soft and hard bounces accurately, as they require different handling strategies. Mailchimp offers a good overview of soft versus hard bounces.
Marketer view
Email Marketer from Email Geeks explains that they recently sent an email announcement to an active and prospecting segment from a newly acquired company, which they had never emailed before. They used a sender address not part of their main domain, resulting in an increase in soft and hard bounces, with error messages like "envelope blocked - User Entry - mimecast SMTP error code 550" and "rejected by header based manually blocked senders."
Marketer view
Email Marketer from Act-On states that monitoring bounces, retrying sends, and utilizing email verification tools are vital steps to maintain a clean list and improve overall deliverability. This proactive approach helps in managing both soft and hard bounce issues effectively.
What the experts say
Experts in email deliverability emphasize that bounce messages like "envelope blocked - User Entry" are clear indicators of recipient-initiated blocks, which are hard bounces and not temporary issues. They stress that such blocks, especially if originating from a new, unvetted list, can severely impact sender reputation. The key advice revolves around rigorous list hygiene, understanding shared sending infrastructure, and proactive reputation management rather than merely changing sender addresses.
Key opinions
- Hard bounce misidentification: Experts explicitly state that "envelope blocked - User Entry" is a hard bounce, meaning the user has manually blocked the sender, and should not be mistaken for a soft bounce.
- Recipient intent: The core message behind these bounces is that the recipients do not wish to receive your mail and have taken direct action to block it.
- Limited impact scope: While recipient blocks affect delivery to those specific individuals, they may not directly cause deliverability issues for other, unaffected recipients unless the volume of blocks is significant enough to trigger broader reputation filters.
- Shared domain risk: If the envelope address is shared across multiple senders (e.g., within an ESP's shared IP or domain pool), a block triggered by one sender can negatively impact all others using that shared resource.
- Unsubscribe analysis: It is advised to investigate if recipients who blocked emails had previously attempted to unsubscribe or showed other signs of disengagement, indicating a deeper problem with consent or relevance.
Key considerations
- Immediate suppression: For any hard bounce (especially user-initiated blocks), the email address must be removed from all future sends immediately to prevent further damage to sender reputation.
- Addressing root cause: Focus on why recipients are blocking your mail. This could stem from poor list acquisition practices (e.g., purchased lists), irrelevant content, or a lack of proper consent.
- Custom envelope domains: Explore options to use a dedicated or custom envelope domain (return-path) to ensure your sending reputation is independently managed and not affected by other senders sharing an IP or domain. Our article on warming up a new sending domain can offer insights.
- Sender reputation preservation: Maintaining a positive sender reputation is critical, and high bounce rates, including persistent soft bounces, can severely impact your ability to reach the inbox. Understanding how hard bounces impact deliverability is essential.
- Proactive list cleaning: Regularly cleaning lists and ensuring consent for all recipients is the best defense against high bounce rates and related deliverability issues. This is especially true when dealing with acquired lists, which can often contain spam traps or unengaged users.
Expert view
Expert from Email Geeks indicates that people explicitly blocked the sender address, and using a different address will only lead to that new address also being blocked. This highlights the futility of simply changing addresses without addressing the core problem.
Expert view
Expert from Spamresource.com explains that high bounce rates, particularly hard bounces, signal to ISPs that your sending practices might be poor. This can inevitably lead to significant reputation damage and hinder future email deliverability.
What the documentation says
Official documentation from various email service providers and deliverability resources consistently highlights the definitions and implications of soft and hard bounces. They underscore the importance of list hygiene, sender reputation, and proper email authentication for maintaining good deliverability. Many resources provide guidelines on how to interpret bounce messages and the necessary steps to take, emphasizing that permanent failures like explicit user blocks require immediate list suppression.
Key findings
- Bounce differentiation: Documentation clearly defines hard bounces as permanent delivery failures (e.g., invalid addresses, explicit blocks) and soft bounces as temporary issues (e.g., full inbox, server downtime).
- Impact on sender reputation: High bounce rates, particularly hard bounces, are consistently cited as detrimental to sender reputation, leading to lower inbox placement and potential blocklisting (or blacklisting).
- List hygiene criticality: Regular list cleaning is a universal recommendation across documentation to minimize bounces and ensure emails reach valid, engaged recipients.
- Authentication importance: Proper email authentication (SPF, DKIM, DMARC) is foundational for proving sender legitimacy and preventing emails from being flagged as spam or blocked outright. A simple guide to DMARC, SPF, and DKIM is available.
- Proactive monitoring: Documentation often advises monitoring bounce rates and other deliverability metrics closely to identify and address issues promptly.
Key considerations
- Hard bounce suppression: Immediately remove hard-bounced email addresses from your mailing list. Many ESPs do this automatically, but it's crucial to confirm and manually intervene if necessary. Learn how to manage hard bounced addresses.
- Soft bounce retry policy: For soft bounces, retrying delivery after a set period is common, but persistent soft bounces (e.g., after several attempts) should also lead to removal or re-engagement campaigns.
- Consent and engagement: Ensure that all recipients have explicitly opted in to receive your emails. Sending to unengaged or old lists is a major cause of bounces and spam complaints.
- Content and reputation alignment: Beyond technical factors, the content of your emails and your overall sender reputation contribute significantly to deliverability. Relevant, desired content reduces user-initiated blocks.
- Continuous monitoring: Continuously monitor bounce rates and other feedback loops. Tools like Google Postmaster Tools provide data to help you improve domain reputation.
Technical article
Mailgun’s documentation on soft bounces clarifies that while they are generally temporary delivery failures, consistent soft bounces can still negatively affect overall deliverability and sender reputation over time, necessitating attention.
Technical article
SendLayer’s guide on hard vs. soft bounces highlights that adhering to email deliverability best practices and maintaining strong list hygiene are crucial to significantly reduce your email bounce rate across all campaigns.
Related resources
15 resources
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