Summary
When encountering 'not our customer' hard bounces, indicated by codes like 5.1.1, from Comcast, the consensus is the email address is invalid. This could be due to typos, account closures, or the address being removed. The most crucial step is to immediately remove these recipients from your mailing list to protect your sender reputation and ensure future deliverability. Implement robust bounce handling that automatically unsubscribes these addresses. Proactively validate email addresses at signup using methods like double opt-in and real-time verification. Maintain good email authentication (SPF, DKIM, DMARC) to prevent your emails from being flagged as spam. Be aware of potential temporary issues causing bounce spikes, and monitor these cases. A high bounce rate signals poor list hygiene to ISPs like Comcast, increasing the likelihood of deliverability issues.
Key findings
- Invalid Address: 'Not our customer' hard bounces indicate an invalid email address.
- Reputation at Risk: Ignoring hard bounces degrades your sender reputation, affecting deliverability.
- Immediate Action: Promptly remove bounced addresses from your mailing list.
- Authentication Matters: Proper email authentication (SPF, DKIM, DMARC) improves deliverability.
- Proactive Validation: Validating email addresses at signup reduces bounce rates.
- Temporary Spikes: Sudden increases may indicate temporary issues; monitor and potentially suppress temporarily.
- 5.1.1 is Standard: 5.1.1 is a standard NDR or SMTP code often representing this type of bounce
Key considerations
- Bounce Management: Invest in a system that automatically processes and removes hard bounces.
- Signup Process: Improve your signup process with double opt-in and real-time verification.
- List Hygiene: Regularly clean your email list to remove inactive or invalid addresses.
- Monitor Performance: Track bounce rates and investigate any unusual increases, especially from specific providers.
- Test ESP Issues: Contact your ESP or test to see if there are broader issues
What email marketers say
12 marketer opinions
When encountering 'not our customer' hard bounces from Comcast, it generally indicates the email address is invalid, potentially due to typos, account closures, or removal. Best practices involve immediately removing these recipients from your list to maintain sender reputation and avoid deliverability issues. Implement robust bounce handling, validate email addresses at signup using double opt-in and real-time verification, and ensure strong authentication protocols (SPF, DKIM, DMARC) are in place. Monitor for temporary spikes, and if suspected, consider temporary suppression with potential re-engagement later. High bounce rates negatively impact deliverability and sender reputation.
Key opinions
- Invalid Address: 'Not our customer' bounces usually mean the email address is invalid.
- Sender Reputation: High bounce rates harm sender reputation, leading to deliverability problems.
- Immediate Removal: Remove hard bounces from your list immediately to protect your sender reputation.
- Authentication: Strong email authentication (SPF, DKIM, DMARC) is crucial for deliverability.
- Temporary Issues: Spikes in bounces might indicate a temporary problem on Comcast's side; monitor and adjust accordingly.
Key considerations
- Bounce Handling: Implement a system to automatically unsubscribe hard-bouncing addresses.
- Address Validation: Validate email addresses at signup to prevent invalid addresses from entering your list.
- Monitoring: Monitor bounce rates and investigate any sudden spikes, especially from specific providers like Comcast.
- ESP Communication: If a large number of bounces occur at once, contact your ESP to see if there are technical issues.
- Testing Re-engagement: If a bounce is suspected to be invalid, consider a single re-engagement to confirm bounce status.
Marketer view
Email marketer from EmailOctopus shares that you need to regularly clean your email list by removing hard bounces. Ignoring hard bounces will increase your bounce rate and damage your sender reputation.
26 Oct 2024 - EmailOctopus
Marketer view
Email marketer from ActiveCampaign shares that after receiving a hard bounce such as “not our customer”, you should immediately remove the recipient from your list to maintain a good sender reputation and avoid future deliverability issues.
27 Feb 2024 - ActiveCampaign
What the experts say
2 expert opinions
Experts agree that a 'not our customer' hard bounce unequivocally signifies an invalid email address at the recipient domain. Continuing to send to these addresses will harm your sender reputation and potentially lead to being blocked. Proper bounce processing, including immediate removal from your mailing list, is essential to prevent deliverability issues.
Key opinions
- Definitive Indicator: 'Not our customer' means the address is invalid.
- Reputation Impact: Sending to these addresses hurts sender reputation.
- Removal is Crucial: Addresses should be immediately removed from the mailing list.
Key considerations
- Bounce Processing: Implement robust bounce processing to handle permanent failures.
- Prevention: Focus on prevention via signup and list hygiene to avoid accumulating invalid addresses.
- Deliverability: Prioritize deliverability by actively managing bounces.
Expert view
Expert from Spam Resource explains that a 'not our customer' hard bounce definitively indicates the email address is invalid at that domain. Continued sending to these addresses will negatively impact your sender reputation and may result in blocking.
6 Nov 2023 - Spam Resource
Expert view
Expert from Word to the Wise, Laura Atkins, shares that proper bounce processing is crucial. 'Not our customer' bounces should be treated as permanent failures, and addresses should be promptly removed from your mailing list to avoid deliverability issues.
24 Jan 2024 - Word to the Wise
What the documentation says
4 technical articles
Technical documentation consistently confirms that a 'not our customer' bounce, often represented by a 5.1.1 NDR or SMTP status code, signifies a permanent delivery failure due to a non-existent email address. These bounces are classified as hard bounces, and attempting to send to these addresses again will negatively impact your sender reputation.
Key findings
- Permanent Failure: 'Not our customer' equals permanent delivery failure.
- 5.1.1 Code: Often indicated by 5.1.1 NDR/SMTP code.
- Reputation Damage: Re-sending damages sender reputation.
Key considerations
- Hard Bounce Handling: Treat as a hard bounce and remove the address from your list.
- Prevention: Implement measures to reduce invalid addresses from entering your system.
- Bounce Monitoring: Monitor bounce rates to identify and address deliverability issues.
Technical article
Documentation from Amazon SES explains that a hard bounce indicates a permanent delivery failure, such as a non-existent email address. Attempting to send to these addresses again will likely result in the same outcome and damage your sender reputation.
6 Nov 2022 - Amazon Web Services
Technical article
Documentation from RFC Editor details that 5.1.1 is a standard SMTP enhanced status code indicating that the recipient address does not exist. It's a permanent error.
2 Oct 2022 - RFC Editor
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