Summary
Email bounces and phishing attacks are significant factors that can severely impact your email deliverability and overall domain reputation. Understanding how these issues manifest and their specific consequences is crucial for maintaining a healthy sending infrastructure and ensuring your legitimate emails reach their intended inboxes.
Key findings
- Temporary vs. permanent bounces: While temporary failures (soft bounces) might not directly harm your reputation, a high volume often signals underlying deliverability problems. Permanent failures (hard bounces, like user unknown) directly damage your sender reputation and lead to blocklistings if not promptly addressed. Regularly removing hard bounces from your lists is paramount.
- Phishing's pervasive impact: Even if phishing attacks aren't originating from your legitimate sending systems, if your domain is being forged or mentioned in phishing content (e.g., in footers or text), it can negatively impact your overall domain reputation. Mailbox providers (MBPs) often use machine learning and manual filters that become wary of domains associated with malicious activity.
- ESP reporting nuances: Different email service providers (ESPs) categorize bounces and blocks differently. It is important to understand their reporting mechanisms, particularly how they differentiate between various bounce types (e.g., temporary, permanent, blocks) and their impact on your standing.
- DMARC protection: Implementing a strong DMARC policy, even at a quarantine level, helps protect your domain from the full reputation impact of forged emails, although it might not completely eliminate the bleed-over effect.
Key considerations
- Identify bounce types: Don't treat all bounces equally. Understand the specific SMTP replies to differentiate between temporary issues and permanent failures like unknown users. This insight helps you prioritize list cleaning efforts and target specific deliverability problems. More on this is available in our guide on hard bounces.
- Maintain rigorous list hygiene: Even with double opt-in, older lists or those not subject to strict verification can contain invalid addresses or spam traps. Regularly cleaning your lists by removing unknown users is critical for improving deliverability and protecting your domain reputation.
- Segment email sending: If you send both transactional and marketing emails, consider using different subdomains or sender identities (e.g., avoid noreply@ for marketing) to prevent issues with one type of mail from contaminating the reputation of the other. This strategy helps isolate potential problems and maintain consistent deliverability. For more on the impact of bounces, refer to this resource from Email Industries.
What email marketers say
Email marketers often grapple with the tangible effects of bounces and phishing on their campaigns. While many implement best practices like double opt-in, the nuances of ESP reporting and the external factors of domain abuse can still pose significant challenges. Marketers seek clarity on how different bounce types are handled and whether their proactive measures are truly sufficient.
Key opinions
- Concern over bounce impact: Marketers frequently express concern that high bounce rates directly harm their deliverability, even if their ESP classifies some as temp fails. There's a perceived disconnect between what ESPs report and the observed impact on delivery rates.
- Desire for granular data: Many marketers find it challenging to classify bounces effectively when reports are at an email address level rather than a campaign level, making it difficult to understand specific problems.
- Confusion over ESP suppression: There's often confusion about how ESPs, like SendGrid, manage suppression lists and how different types of bounces (especially blocks) are handled compared to proper bounces.
- Phishing impact on legitimate mail: Marketers are often unaware of how their domain being used in unrelated phishing attacks (e.g., by third-party services) can still impact the deliverability of their legitimate transactional or marketing emails, even with robust internal security.
Key considerations
- Verify ESP bounce classifications: Do not assume your ESP's bounce and block classifications fully align with standard deliverability best practices or the actual impact on your reputation. Always seek deeper insights into the underlying SMTP replies. For details on how bounces affect domain reputation, refer to this article on understanding domain reputation.
- Proactive list cleaning: Implement robust list hygiene practices that go beyond initial double opt-in. Regularly remove all hard bounces (user unknown) and actively manage blocks to mitigate negative reputation impacts. High bounce rates can significantly damage sender reputation and lead to deliverability problems, as explored in articles like The Hidden Costs of Email Bounces.
- Monitor your domain's wider use: Be aware of any external abuse of your domain (e.g., phishing campaigns, even by third parties). While you might not control these entirely, being informed helps you understand potential reputation challenges and enables you to make strategic decisions, such as separating marketing and transactional sending domains. Learn more about how email sending practices impact domain reputation.
Email marketer from Email Geeks notes that they are observing a lower and lower delivery rate for a specific newsletter, which has dropped to 95%. They consider this rate suboptimal and are actively seeking explanations for the decline. This indicates a proactive approach to monitoring and improving email performance.The marketer consistently cleans all their email lists and employs a double opt-in process for all new audience groups, including the problematic newsletter. This ensures that new sign-ups provide correct email addresses, minimizing initial bounce risks. Despite these efforts, the delivery rate continues to decline, suggesting other underlying issues may be at play. They seek external advice to pinpoint additional factors affecting deliverability beyond list hygiene.
An email marketer from Email Geeks raises a question about high bounce rates and their direct impact on deliverability. Their ESP, SendGrid, asserts that only blocks within the overall bounce category negatively affect deliverability, not proper bounces. This distinction from their ESP leads to confusion and a request for clarification from deliverability experts.This inquiry highlights a common challenge marketers face in interpreting ESP reports and understanding the true implications of different bounce classifications. The marketer is trying to reconcile their intuition about deliverability with the information provided by their service provider. They are seeking to confirm if this classification method (where only blocks are impactful) is indeed accurate across the industry.
What the experts say
Deliverability experts provide critical insights into the complex relationship between bounces, phishing, and domain reputation. They highlight that not all bounces are equal in their impact and emphasize the often-overlooked threat of domain abuse (phishing) on legitimate email streams. Their consensus points to the need for granular data analysis and a holistic view of sending health, extending beyond internal practices.
Key opinions
- Bounce types matter: Temporary failures may not directly harm reputation but act as a warning signal. Permanent failures, particularly user unknown bounces, are a direct negative deliverability factor. Each MBP might treat different bounce types with varying impacts.
- Phishing's severe domain impact: The prevalent use of a domain in phishing or malware campaigns (even via third-party services) can severely degrade its overall reputation. Machine learning and manual filters become wary of such domains, affecting legitimate mail deliverability, especially at smaller mailboxes.
- DMARC's role in mitigation: While DMARC can help insulate a domain from the full brunt of reputation hits caused by forged messages (especially with a quarantine policy), it may not completely prevent bleed-over reputation issues, particularly if the legitimate domain is mentioned in phishing content.
- Importance of SMTP replies: Relying on generic bounce reports from ESPs isn't sufficient. Senders need to dig into specific SMTP replies to understand the true reason for bounces and the underlying reputation signals (e.g., Yahoo's TS or TSS responses indicate existing poor reputation). This is why understanding reputation drops is critical.
Key considerations
- Action user unknown bounces: Actively remove addresses that consistently return a 550 user unknown response. These signal attempts to mail bad addresses, which negatively impacts reputation. This applies even if you use soft bounce retry policies.
- Separate sending identities: Avoid using noreply@ for marketing newsletters, especially if that address is commonly abused in phishing. Distinct sending domains for different mail streams can help isolate reputation issues.
- Investigate all high bounces: Dig deeper into the specific types of high bounces you're experiencing. A generic bounce count from your ESP doesn't provide enough information to resolve underlying deliverability problems. Getting specific error messages is crucial. For further reading, Mailjet's blog on IP reputation offers insights into related factors.
Email expert from Email Geeks explains that if bounces are merely temporary failures in a report, they do not directly harm your sender reputation. These types of bounces, such as a mailbox being full, are often transient issues that resolve themselves. Therefore, while frustrating, they aren't inherently indicative of a permanent negative mark against your sending domain or IP.However, the expert emphasizes that a high volume of such temporary failures should still be seen as a giant, flashing light that your overall reputation is in a poor state. A significant number of soft bounces indicates a persistent underlying problem, such as an unengaged list or a sender that is not adequately warmed up, which ISPs might interpret as problematic behavior over time.
Email expert from Email Geeks states that the user's domain is experiencing heavy abuse, specifically noting dozens of forgeries occurring weekly. These forged emails are being sent to addresses that have been harvested from websites. This direct observation suggests a significant security vulnerability or a widespread spoofing issue affecting the domain's reputation externally.They clarify that these are not merely emails being marked as phishing, but are genuine phishing attempts. This distinction is critical because it indicates a real and ongoing threat that directly impacts the domain's standing with mailbox providers, regardless of the sender's legitimate email practices.
What the documentation says
Official documentation and research often align on the fundamental principles of email deliverability, emphasizing the critical role of managing bounces and preventing phishing to preserve domain reputation. They highlight that high bounce rates are a strong negative signal, while any association with malicious activity, even indirect, can compromise a sender's trustworthiness in the eyes of mailbox providers.
Key findings
- Bounce rate as reputation indicator: Documentation consistently shows that high bounce rates, particularly hard bounces, are a primary factor in the degradation of sender reputation. They signal poor list quality and can lead to emails being sent to spam or outright blocked.
- Impact of spam complaints: Alongside bounces, documentation frequently cites spam complaints as a direct and severe negative impact on IP and domain reputation. These complaints explicitly tell mail providers that recipients do not want your emails.
- List hygiene importance: Official guides stress the necessity of regular email list cleaning to remove invalid or inactive addresses. This practice is crucial for reducing bounces and avoiding spam traps, which can swiftly lead to blocklisting. This is why tools like our Email Deliverability Tester are important.
- Phishing and domain association: Even if not directly originating from a sender's infrastructure, instances of a domain being exploited for phishing or malware can negatively influence its perceived trustworthiness by recipient systems. This often leads to increased scrutiny and potential filtering of legitimate emails.
Key considerations
- Prioritize bounce rate reduction: Implementing strategies to reduce bounce rates is consistently highlighted as a top priority for maintaining domain reputation and achieving high deliverability. This includes thorough list validation and prompt removal of bounced addresses, as explored in the Benchmark Email guide on reducing bounce rate.
- Implement strong authentication: Beyond managing bounces, documentation consistently recommends robust email authentication protocols such as SPF, DKIM, and DMARC. These measures help verify sender identity and prevent domain spoofing, thereby protecting reputation from phishing attacks.
- Monitor blocklists: Regular monitoring of email blocklists and blacklists is advised to quickly identify if a domain or IP has been listed due to high bounces, spam complaints, or phishing, allowing for prompt remediation. Our blocklist monitoring can help with this.
Documentation from Email Industries states that high bounce rates are a significant detriment to sender reputation, ultimately leading to various deliverability issues. This underscores the fundamental principle that mail servers interpret frequent delivery failures as a sign of poor list quality or abusive sending practices, negatively impacting how subsequent emails are received.To counteract this, the documentation advises consistent email list management and proper authentication. These measures are presented as essential tools for reducing bounce rates, improving sender reputation, and ensuring emails reach the inbox effectively. The emphasis is on proactive hygiene to maintain sender trustworthiness.
Documentation from Mutant Mail highlights that reducing bounce rates is a crucial step for maintaining a healthy domain reputation and achieving high email deliverability. This reinforces the direct correlation between the cleanliness of an email list and the sender's perceived trustworthiness by recipient servers. Low bounce rates signal a responsible sender.One effective strategy suggested for minimizing bounces is through rigorous list management practices. This includes regularly validating email addresses and promptly removing invalid or inactive ones. By ensuring emails are only sent to legitimate and active recipients, senders can significantly improve their deliverability rates and protect their domain's standing.
