Understanding and Resolving Email Blacklisting Issues

1. Email Blacklisting: Causes and Consequences

When sending emails, your IP addresses can be blacklisted by email blacklists and email providers like Google and Outlook/Exchange Online. This typically occurs because your emails are not well-qualified; they are flagged as spam by recipients or because you are sending emails to non-existent addresses. Blacklisting can significantly hinder your email deliverability, causing legitimate emails to be blocked or rejected.


550 5.7.1 Unfortunately, messages from [172.246.xx.xx] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [DB8EUR05FT049.eop-eur05.prod.protection.outlook.com 2024–06–26T06:37:01.176Z 08DC95A44C5BD80E]

2. Diagnosing Rejected Emails

If you notice that your emails are being rejected, it is crucial to determine the cause. This can be done by analyzing the data in your Google Postmaster instance, particularly the delivery errors tab :

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Additionally, checking the SMTP logs produced by your email sending system can provide insights into why emails are being rejected :

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These logs often contain error codes and messages that can help identify the specific issues leading to rejection.

3. Adhering to Good Email Sending Practices

Once you understand why your emails have been blocked and classified as spam, it’s essential to conform to good email sending practices. Following the sender guidelines provided by Google and other email providers can help improve your email deliverability. These guidelines typically include best practices for maintaining email list hygiene, authenticating your email (using SPF, DKIM, and DMARC), and crafting emails that are less likely to be marked as spam.

You can use tool like mail-tester.com to check the quality of your e-mails :

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4. Contacting Blacklist Authorities

After implementing best practices, it’s advisable to contact the blacklists that have blacklisted your IP and domain. Many blacklists and email providers, including Google and Outlook, offer sender support forms to request removal from their blacklists. You can access these forms through the following links:

5. Proactive Monitoring and Alerts

To ensure you are promptly informed of any delivery issues, consider using a solution like DMARC EXPERT that alerts you whenever your emails do not adhere to good sender practices. This proactive approach can help you quickly address and resolve any issues, maintaining a high standard of email deliverability and avoiding future blacklisting.

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By understanding the causes of blacklisting, diagnosing issues accurately, adhering to best practices, and actively managing your sender reputation, you can significantly improve your email deliverability and ensure that your messages reach their intended recipients.