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.
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.
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.
16 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.
17 Feb 2024 - ActiveCampaign
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.
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.
27 Oct 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.
14 Jan 2024 - Word to the Wise
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.
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.
27 Oct 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.
22 Sep 2022 - RFC Editor
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