IP blacklisting occurs for a multitude of reasons encompassing technical vulnerabilities, poor sending practices, and shared infrastructure risks. Infections relaying spam from your network, sending mail from behind a NAT (Network Address Translation) particularly when other services are also using the same NAT IP, inconsistent sending volumes, high spam complaint rates, sending to invalid email addresses, and poor email authentication are all contributing factors. In shared hosting environments, the actions of other users can negatively impact your IP's reputation. Addressing blacklisting requires identifying the specific blacklist, understanding the reason for the listing, resolving the underlying issues, and then requesting delisting. Proactive measures include monitoring blacklist status, maintaining clean email lists free of spam traps, implementing email authentication (SPF, DKIM, DMARC), securing mail servers to prevent open relaying, gradually warming up new IPs, and utilizing feedback loops to manage spam complaints.
9 marketer opinions
An IP address can be blacklisted for numerous reasons related to email sending practices. Common causes include high spam complaint rates, sending to invalid email addresses (high bounce rates), poor email authentication (SPF, DKIM, DMARC), and the presence of spam traps in the recipient list. Blacklists monitor these factors and list IPs that exceed established thresholds. Shared hosting environments can also lead to blacklisting due to the actions of other users on the same server. Addressing blacklisting requires identifying the specific blacklist, determining the reason for listing, resolving the underlying issues, and requesting delisting. Proactive measures include monitoring blacklist status, maintaining clean email lists, warming up new IPs gradually, and securing mail servers to prevent open relaying.
Marketer view
Email marketer from SendPulse explains that if you're using a new IP address, gradually warm it up by sending small volumes of email to engaged subscribers first. Gradually increase the volume over time to establish a positive sending reputation. Sudden large volumes of email from a new IP can trigger blacklisting.
28 Nov 2021 - SendPulse
Marketer view
Email marketer from Digital Ocean explains that the steps to remove an IP address from a blacklist typically involve identifying the blacklist, determining the reason for listing, resolving the issue (e.g., stopping spamming activity, fixing authentication), and then requesting delisting from the blacklist provider. Each blacklist has its own delisting process.
21 Apr 2025 - Digital Ocean
5 expert opinions
IP blacklisting can occur due to various technical and behavioral reasons. Underlying infections relaying spam, sending from behind a NAT (especially when combined with other machines), and inconsistent sending volumes are significant contributors. Identifying the specific blacklist is crucial for understanding the cause and initiating the delisting process. Implementing feedback loops (FBLs) helps monitor and manage spam complaints. Using a dedicated mail server with a real IP address is recommended over sending mail from behind a NAT.
Expert view
Expert from Word to the Wise explains the importance of feedback loops (FBLs). FBLs allow you to receive reports about spam complaints from email providers. By subscribing to FBLs, you can identify and remove users who are marking your emails as spam, thus reducing the risk of blacklisting.
22 Sep 2022 - Word to the Wise
Expert view
Expert from Spam Resource shares that identifying which blacklist your IP is on is the first step. Use a multi-RBL lookup tool like MXToolbox to check your IP against multiple blacklists simultaneously. Knowing which blacklist has listed you helps you understand the specific reason and delisting process.
10 Apr 2023 - Spam Resource
4 technical articles
IP addresses are blacklisted for various reasons, including sending spam, hosting malware, or being part of a botnet. Identifying if you are on a blacklist and why is the first step, which can be done using tools like Spamhaus and MultiRBL. Maintaining a good IP reputation is crucial, as reflected by your sending history, and can be monitored using tools like MXToolbox. Adhering to SMTP standards outlined in RFC 5321 ensures proper email sending practices and helps avoid being flagged as spam.
Technical article
Documentation from RFC 5321 explains that the SMTP (Simple Mail Transfer Protocol) standards document outlines best practices for email sending, including proper HELO/EHLO greetings, message formatting, and error handling. Adhering to these standards helps ensure deliverability and avoid being flagged as spam.
20 Dec 2024 - RFC Editor
Technical article
Documentation from MultiRBL explains that MultiRBL is a tool to check if your IP address is listed on multiple DNS-based blacklists (DNSBLs) or Realtime Blackhole Lists (RBLs). It provides a consolidated view of your IP's status across various blacklists, helping you identify if you're listed and on which lists.
4 Nov 2021 - MultiRBL.valli.org
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