How can I prevent my domain from being blacklisted due to an infected employee's computer or scraping contact information?

Key findings

• Header visibility: Personal Wi-Fi or mobile carrier IPs can appear in email headers if an employee's client connects directly to a corporate mail server (MTA) without intermediate filtering or header stripping. This exposes the initial connection IP.
• Malware impact: An infected employee's computer can send malware or spam through your corporate smart host, leading to your domain or primary sending IP being blacklisted, even if the infected machine's IP is dynamic.
• Scraping risks: Using software that automatically gathers (scrapes) email addresses from public websites for unsolicited outreach, such as link-building campaigns, is widely considered spamming and can lead to severe deliverability issues and blocklisting, regardless of email volume.
• Domain reputation over IP: Even if the specific external IP is not yours, if your domain is associated with problematic sending behavior, email filters like Mimecast can block all emails from your domain.
• Support limitations: Tier-one support at ISPs or email filtering services may provide limited or inaccurate information regarding complex deliverability issues.

Key considerations

• Employee security: Implement robust endpoint security measures and educate employees on safe internet practices to prevent malware infections on corporate devices, especially when using external networks.
• MTA configuration: Configure your Mail Transfer Agent (MTA) to strip or modify internal client IPs from outbound email headers. This can prevent external blocklists from associating your domain with potentially problematic dynamic IPs. Learn more about how to manage senders and identify the cause during an email blacklisting.
• DMARC policy enforcement: DMARC policy (e.g., p=quarantine or p=reject) to prevent any potential abuse of your domain for sending emails, which could lead to blocklists.
• Ethical email acquisition: Avoid scraping email addresses. Focus on building permission-based lists through explicit consent (opt-in) to ensure legitimate engagement and protect your sender reputation. The FTC provides guidance on CAN-SPAM compliance related to email marketing practices.
• Proactive monitoring: Regularly monitor your domain and IP for blocklist listings. If a listing occurs, immediately investigate the cause by reviewing mail logs and identifying any unusual sending patterns or compromised accounts.

Key opinions

• IP confusion: Marketers are often puzzled when their domain is blocked due to an IP address that they don't directly control or recognize as part of their sending infrastructure.
• Mimecast sensitivity: There's a perception that Mimecast, in particular, can be very aggressive or unique in its blacklisting triggers compared to other ISPs or filters.
• Wi-Fi risk: A concern exists that an employee using corporate email on an external Wi-Fi connection (like a coffee shop) could inadvertently compromise the domain's sending reputation if that Wi-Fi IP is problematic.
• Header visibility: Some marketers are surprised to learn that an employee's internet connection IP can appear in email headers, potentially affecting their domain's standing with mail filters.
• Scraping perception: Marketers using SEO tools that scrape public email addresses for outreach often believe this practice is standard for link building, not spam, assuming that publicly available role accounts like info@ are meant for general queries.

Key considerations

• Investigate all IPs: Don't dismiss the listed IP, even if it's not your main MTA. Understand how it's linked to your domain and why it's appearing in headers. This is part of identifying the true cause of a blacklist.
• MTA configuration review: Work with DevOps to adjust MTA settings to prevent sensitive internal IPs (like client connection IPs) from being included in outbound mail headers, if not necessary for legitimate tracking. This can include using settings to hide message sources.
• Holistic view of reputation: Recognize that a blocklist by one major filter can indicate a broader underlying issue, even if other ISPs haven't yet reacted. Domain reputation is complex and affects all sending. Read our guide on understanding your email domain reputation.
• Address underlying spam triggers: Re-evaluate email acquisition methods. If using scraped lists, even for low-volume outreach, understand that this is a common spam trigger that can lead to blacklisting. Consider the legal implications, particularly for US-based campaigns, regarding CAN-SPAM Act compliance.

Key opinions

• Malware is primary suspect: A common cause for blacklisting is an employee's machine being infected with malware that then sends spam or malware through the company's mail server (smart host).
• Header analysis for diagnosis: Mail filters may look beyond the immediate SMTP connection IP and consider IPs in Received from: headers for reputation, especially in specific or unusual configurations. However, if the main outbound IP is blocked, it's likely due to malware originating from that IP, not just the client's home network IP.
• Strip internal IPs: It is a recommended best practice for MTAs to strip out or replace client connecting IPs (especially RFC1918 addresses or dynamic ISP IPs) from outbound messages to prevent them from affecting overall domain reputation. Options like hide-message-source or remove-header in PMTA can be used.
• Unsolicited email is spam: Experts unequivocally define mechanical scraping of email addresses and sending unsolicited messages (like link-building outreach) as spam, regardless of the perceived value or low volume. This activity alone can be grounds for blacklisting.
• Legal ramifications: In jurisdictions like the US, sending unsolicited commercial email that fails to comply with regulations like CAN-SPAM, especially when addresses are scraped, can lead to legal penalties.

Key considerations

• Prioritize malware remediation: If a mail filter indicates malware, it should be taken seriously. The most critical step is to identify the infected machine using mail logs (cross-referencing timestamps and IPs with authenticated users) and clean it immediately. This is the only way to recover from certain blocklistings like those involving compromised accounts.
• DMARC adoption: Updating a DMARC policy from p=none to p=quarantine or p=reject can help prevent unauthorized use of your domain and protect against potential abuse by external entities or compromised internal systems. Our guide to DMARC, SPF, and DKIM can provide further insight.
• Review email acquisition: Companies must critically assess their list-building practices. Mechanically harvesting email addresses from public sources, especially for unsolicited communication, is a significant deliverability risk. Even if perceived as link building, it violates anti-spam norms and often legal requirements. This is key to long-term deliverability success, as discussed in our article on spam traps.
• Monitor SMTP logs: Actively monitoring outgoing mail at the SMTP level, particularly for unusual volumes or patterns associated with specific users or IPs, can help detect and prevent issues before they escalate to widespread blacklisting. This helps in understanding what happens when your IP gets blocklisted.

Key findings

• Security scans are vital: Regular security scans are recommended to monitor for malware and unauthorized activity that could lead to a domain being blacklisted. This proactive detection helps in early remediation.
• Data scraping impacts deliverability: Automated data scraping of email addresses is identified as a method for acquiring contacts without consent, often leading to unsolicited email, which Internet Service Providers (ISPs) and mail filters actively block.
• Rate limiting: Implementing rate limits on requests from IP addresses can protect websites from exploitation, including malicious scraping activities, by controlling the volume of interactions within a given timeframe.
• Strong authentication prevents abuse: Measures like DMARC, SPF, and DKIM are crucial for email authentication, preventing bad actors from spoofing your domain or sending unauthorized mail through your infrastructure.
• Internal monitoring: Monitoring employee computer activity can help identify misuse of company resources or compromised devices that might be contributing to deliverability issues.

Key considerations

• Comprehensive security: Ensure your internal network and employee devices are protected with up-to-date antivirus software, firewalls, and regular security audits to prevent malware outbreaks that could affect email sending.
• Adherence to email best practices: Always obtain explicit consent before adding email addresses to your mailing lists. Avoid any practices that involve automated harvesting of contacts, as this directly contributes to a poor sender reputation and blacklisting.
• MTA hardening: Configure your Mail Transfer Agent (MTA) with security features that prevent the leakage of potentially reputation-damaging client IPs in email headers. This often involves specific settings to redact or sanitize received headers.
• Implement DMARC: Properly implement and monitor DMARC records to gain visibility into email authentication failures and prevent unauthorized use of your domain in email, a key step in protecting your domain reputation.