Summary
A valid email address may hard bounce due to various reasons, including DNS issues, problems with the recipient's email infrastructure (like Gmail), sender errors, ESP errors, greylisting, temporary server issues, overly aggressive spam filters, or even false positives. It's often difficult to pinpoint the exact cause without access to detailed logs. Resolving and preventing hard bounces involves maintaining a clean email list through double opt-in, regular scrubbing, segmentation, and re-engagement of inactive subscribers. Utilizing email validation tools, checking SMTP bounce codes, contacting recipients via alternative channels, and resending emails are also recommended. Overall, a continuous effort in list hygiene and deliverability monitoring is crucial.
Key findings
- Multitude of Causes: Hard bounces can stem from a wide range of technical issues, including DNS problems, server errors, greylisting, and spam filtering, as well as incorrect list management.
- Diagnostic Complexity: Identifying the specific reason for a hard bounce is often challenging and may require access to detailed email server logs.
- False Positives Occur: Some hard bounces are false positives, particularly with Gmail addresses, suggesting that immediate removal isn't always the best course of action.
- List Hygiene is Key: Maintaining a clean email list through various methods like double opt-in and regular scrubbing is crucial for minimizing hard bounces.
- Validation Tools Help: Email validation tools can proactively identify invalid addresses, reducing the likelihood of hard bounces.
Key considerations
- Implement Double Opt-in: Use double opt-in to ensure subscribers genuinely want to receive emails and that their email addresses are valid.
- Scrub Your List Regularly: Perform regular list cleaning, especially if you haven't emailed your list in a while, to remove inactive or invalid addresses.
- Use Validation Tools: Employ email validation tools to identify and remove invalid email addresses before sending.
- Understand Bounce Codes: Familiarize yourself with SMTP bounce codes to better understand the reasons behind hard bounces.
- Contact Recipients When Possible: When feasible, contact recipients through other means to confirm their email address and troubleshoot server issues.
- Monitor Reputation: Consistently monitor your sender reputation to ensure it's not negatively impacted by excessive bounces.
- Implement Feedback Loops: Set up feedback loops with ISPs to receive information about bounce messages and spam complaints.
- Resend & Check Spam: If a Gmail address bounces, try resending and advising the recipient to check their spam folder, as it might be a false positive.
What email marketers say
12 marketer opinions
A valid email address may hard bounce due to various reasons, including DNS issues, recipient server problems, sender errors, ESP errors, or false positives. Resolving hard bounces involves maintaining a clean email list through double opt-in, regular scrubbing, and utilizing email validation tools. Immediate removal of hard-bounced addresses, segmentation of lists, and re-engagement of inactive subscribers are also recommended. Addressing typos, checking sender reputation, and contacting recipients via alternative channels can also help mitigate hard bounce issues.
Key opinions
- Hard Bounce Reasons: Hard bounces can result from several issues: invalid addresses, server problems, DNS issues, sender errors, and ESP errors.
- False Positives: Some hard bounces are false positives, especially with Gmail addresses. Resending the email or checking the spam folder may resolve this.
- Email List Cleaning: Regularly scrubbing your email list is crucial for maintaining deliverability and avoiding hard bounces.
- Email Validation Tools: Email validation tools detect invalid, misspelled, or inactive addresses before sending, preventing hard bounces.
- Double Opt-In: Implementing a double opt-in process ensures the email address is valid and the subscriber wants to receive emails, reducing hard bounces.
Key considerations
- Immediate Removal: Immediately remove hard-bounced addresses from your list to protect your sender reputation.
- List Segmentation: Segment your email list and re-engage inactive subscribers to maintain a clean and active list.
- Address Typos: Double-check email addresses for typos and use confirmation emails to prevent errors.
- Sender Reputation: Maintain a good sender reputation by avoiding sending to invalid or inactive addresses.
- Alternative Contact: If possible, contact the recipient through another channel to confirm their email address and server status.
Marketer view
Email marketer from SendPulse explains that a hard bounce happens when an email can’t be delivered for permanent reasons, like an invalid or non-existent email address. It recommends immediately removing hard bounced addresses from your subscriber list to maintain a good sender reputation.
7 Dec 2022 - SendPulse
Marketer view
Marketer from Email Geeks suggests that the problem is often on the sender's side, claiming that many bounced email lists contain a significant percentage of valid email addresses, and identifies numerous reasons why these bounces occur. He recommends resending the email to see if it's received.
15 Jun 2024 - Email Geeks
What the experts say
3 expert opinions
Diagnosing the reason for a hard bounce on a valid email address can be difficult, often requiring access to detailed logs that may still not provide a clear answer. Several factors can contribute, including greylisting, temporary server issues, or aggressive spam filtering. Maintaining a clean and up-to-date email list is also emphasized as a continuous process essential for a good reputation and deliverability. Direct communication with the recipient to verify their address and server status is also a recommended action.
Key opinions
- Diagnostic Difficulty: Determining the cause of a hard bounce can be challenging and may require log access.
- Possible Causes: Greylisting, temporary server issues, and aggressive spam filters can all cause hard bounces.
- List Maintenance: Ongoing list cleaning is crucial for maintaining deliverability.
Key considerations
- Check Logs: Examine error logs for potential clues about the cause of the bounce.
- Continuous Cleaning: Make list cleaning an ongoing process, not a one-time event.
- Direct Communication: Contact the recipient directly to verify their email address and server status.
Expert view
Expert from Spam Resource explains that there could be several reasons for a valid email address to hard bounce, including greylisting issues, temporary server problems on the recipient's end, or overly aggressive spam filters. They suggest checking error logs and contacting the recipient via other means to confirm their address is active.
25 Mar 2025 - Spam Resource
Expert view
Expert from Email Geeks states it's often impossible to definitively determine the cause of a hard bounce without access to detailed logs, and even then, the cause might remain unclear. He adds that while Sailthru is a reputable ESP, lower-tier support staff may not have the expertise to accurately diagnose the problem.
27 Jan 2023 - Email Geeks
What the documentation says
4 technical articles
Documentation from various sources indicates that a hard bounce represents a permanent email delivery failure, typically due to an invalid or non-existent email address. To resolve this, regular email list cleaning is recommended, along with implementing feedback loops to handle bounces effectively. Understanding SMTP bounce codes can help diagnose the reasons behind hard bounces. Additionally, checking for domain existence, email address validity, recipient server connectivity, and contacting the recipient through alternative channels can assist in resolving bounce issues.
Key findings
- Permanent Failure: Hard bounces indicate a permanent failure to deliver an email.
- Invalid Addresses: Hard bounces often result from invalid or non-existent email addresses.
- Diagnosis via Codes: Understanding SMTP bounce codes can help diagnose hard bounce causes.
- Server Issues: Recipient server issues can also lead to hard bounces.
Key considerations
- List Cleaning: Clean your email list regularly to remove hard bounces.
- Feedback Loops: Implement feedback loops to handle bounces effectively.
- Check Domain and Address: Verify domain existence and email address validity.
- Alternative Contact: Contact the recipient through another method to confirm their email address is active and server is functioning.
Technical article
Documentation from Google Support explains that sometimes issues with the recipient's email server can cause bounces. If you know the recipient, try contacting them through another method to confirm their email address is active and that their server is functioning correctly.
22 Sep 2023 - Google Support
Technical article
Documentation from Mailjet explains that a hard bounce indicates a permanent failure to deliver an email. This usually occurs because the email address is invalid or doesn't exist. They suggest cleaning your email list regularly to remove hard bounces.
26 Jan 2022 - Mailjet
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