How does an IP address being on a blocklist affect domain reputation and email open rates?

Key findings

• Direct impact: An IP address on a blocklist (or blacklist) will cause emails sent from that IP to be blocked, sent to spam, or heavily throttled by recipient mail servers.
• Indirect domain effect: While the domain itself might not be directly blocklisted, if the IP address is actively used for sending emails associated with the domain, the poor IP reputation can negatively influence the domain's overall sending reputation. This relationship is further explored in our guide on IP and domain reputation differences.
• Shared IP challenges: On shared IP addresses, the sending practices of other users can impact your own deliverability, even if your practices are sound. A single problematic IP within a shared range can affect the collective reputation of that range.
• Open rate decline: When emails are blocked or diverted to spam folders due to IP blocklisting, they are not seen by recipients, directly leading to a decline in email open rates.
• Historical listings: Some blocklist entries are historical and may pertain to past misuse of an IP. If the IP is no longer actively sending mail for your domain, its listing might not be the primary cause of current deliverability issues.

Key considerations

• Verify IP usage: Confirm whether the blocklisted IP is indeed being used by your domain for email sending. Diagnostic tools might show associated IPs that are not primary senders.
• Review ESP practices: If using a shared IP with an Email Service Provider (ESP), understand their management of IP reputation and blocklist remediation. Learn what happens when your IP gets blocklisted.
• Focus on root causes: Low open rates often stem from multiple factors, including sender reputation, content quality, and list hygiene. A blocklisted IP might be a symptom, not the sole cause. A helpful resource on this is Mailgun's article on how to get off an email blocklist.
• Proactive monitoring: Regular monitoring of your sending IPs and domain on various blocklists is essential for early detection and swift action.

Key opinions

• Performance impact: Marketers directly experience the consequence of blocklisting through declining email open rates and overall campaign effectiveness.
• Diagnostic difficulty: There's a common struggle to determine if a blocklisted IP, particularly one discovered through a general search, is genuinely impacting their specific email sending from a given domain. They often ask why their emails are going to spam.
• Shared IP confusion: Uncertainty exists around how a single IP on a blocklist affects other IPs or the broader domain, especially when using ESPs that manage shared IP pools.
• Seeking connections: Marketers often try to connect observed deliverability issues, like low open rates, to any potential negative indicators they find, such as an IP blocklist entry.

Key considerations

• Trace the IP: It's crucial for marketers to accurately identify the sending IP addresses used by their domain for email. Tools like MXtoolbox can be misleading if the IP is not actively used for email by the domain.
• Understand shared environments: When using shared IPs, marketers need to be aware that the actions of others can impact their deliverability, requiring them to push their ESP for better IP hygiene. More details are available on IP reputation and its importance.
• Distinguish IP vs. domain: While IP reputation affects deliverability, understanding the separate but linked role of domain reputation is vital. Read our article on how sending practices affect reputation.
• Beyond the blocklist: Marketers should look beyond a single IP listing and consider a holistic view of their email program, including content, list quality, and authentication (SPF, DKIM, DMARC).

Key opinions

• IP origin is crucial: Experts highlight the need to verify where the IP address came from and if it's truly associated with legitimate email sending for the domain in question. This involves checking PTR records and IP ranges.
• Historical listings matter: An IP blocklist entry dating back several years, especially if tied to old malware or a previous occupant, might not be the cause of current deliverability problems if the IP is no longer used by the sender for mail. However, such listings still warrant attention for general IP hygiene.
• ESPs' responsibility: For shared IPs, experts often point to the ESP's (e.g., Microsoft's) responsibility to manage their IP reputation and actively request delistings when historical or irrelevant entries appear. This is critical for preventing issues like IP range behavior impacting other IPs.
• Direct mail usage validation: It's critical to determine if a blocklisted IP is _actually_ being used for mail sending by the affected domain before assuming a direct correlation to deliverability issues. Without this confirmation, the blocklist entry might be irrelevant to email flow.

Key considerations

• Contextualize blocklist data: Always consider the age and reason for an IP blocklist entry. Not all entries are current or relevant to an active email program. A specific blocklist, like SpamRats blacklist relevance, should be evaluated for impact.
• Address IP reputation directly: If the IP is active, engage with the blocklist operators or your ESP for delisting. A large provider like Microsoft having many listings suggests systemic issues they need to address.
• Evaluate diagnostic tools: Be critical of information from general lookup tools. They may provide data points that are technically accurate but irrelevant to current email deliverability. Sometimes they are how email blacklists actually work.
• Proactive IP management: Consider if a change in IP address or ESP strategy is needed if persistent issues with shared IPs negatively impact your sender reputation.

Key findings

• IP reputation as a trust score: IP reputation is widely described as a measure of trustworthiness for an email sender's IP address, directly influencing acceptance by recipient mail servers.
• Blocklists' function: Email blocklists (or blacklists) are databases that list IP addresses or domains identified as sources of spam or malicious email. Their purpose is to prevent unwanted mail from reaching inboxes. To learn more, read our guide on what an email blacklist is.
• Cascading impact: A blacklisted IP can lead to immediate email rejections or diversions to spam folders, resulting in a direct drop in open rates and engagement metrics. This affects how bounces affect email deliverability.
• Domain reputation override: Some documentation suggests that a poor domain reputation can sometimes override the impact of individual IP addresses, meaning emails might still land in spam even if the IP is clean, if the domain is not trusted.

Key considerations

• Sender compliance: Adherence to best practices for email sending, including maintaining clean subscriber lists, avoiding spam traps, and prompt processing of opt-outs, is paramount to maintaining good IP and domain reputation.
• Authentication standards: Implementing and properly configuring email authentication protocols like SPF, DKIM, and DMARC is critical for verifying sender identity and building trust, which can mitigate the impact of some reputation issues. Read about how DMARC impacts deliverability.
• Prompt delisting: If an IP is legitimately blocklisted, documentation advises prompt action for removal by following the specific procedures of the blocklist operator. This is also covered in how to resolve domain blocklisting.
• Holistic view: A comprehensive approach to email deliverability involves continuous monitoring of both IP and domain reputation, alongside content and list quality, to ensure optimal inbox placement.