What could cause unfamiliar IP addresses to appear in PMT, and what steps should be taken to investigate?

Key findings

• Unauthorized sending: Unexpected IPs often point to SaaS products or forgotten SMTP connectors within your organization sending emails using your domain. This can lead to a blocklist or blacklist listing for an IP address if not handled correctly.
• Spoofing or forgery: Someone might be forging your domain, possibly even passing SPF (Sender Policy Framework) authentication, making them appear legitimate in PMT.
• Infrastructure changes: Recent migrations of internal mail servers or changes in your email service providers (ESPs) can introduce new, legitimate IPs that simply haven't been accounted for.
• PMT reporting threshold: The volume of emails from a previously unnoticed or low-volume source might have suddenly crossed Google Postmaster Tools' reporting threshold, making these IPs visible for the first time.
• DNS inconsistencies: Mismatched PTR (pointer) and A (address) records, or IPs associated with domains using privacy services, are common red flags indicating suspicious activity or misconfiguration.
• Snowshoe spam: The presence of many unfamiliar IPs could indicate a 'snowshoe spam' tactic, where spammers distribute low-volume mail across numerous IPs and domains to evade detection.

Key considerations

• DMARC reports: Utilizing DMARC reports is paramount. They provide aggregate data detailing all IPs sending mail as your domain, along with authentication results, which is crucial for identifying unauthorized senders.
• Security team involvement: Engage your internal security teams. They can leverage network monitoring tools to trace outbound traffic from suspicious IPs and assess potential attacks against your customers.
• Abuse team consultation: Collaborate with your abuse team for deeper analysis, as they possess specialized tools and expertise in handling incidents of domain misuse or email abuse.
• DNS verification: Thoroughly check PTR and A records for all identified IPs. Inconsistencies are a major red flag for malicious activity. For more information about understanding your PMT data, refer to our ultimate guide to Google Postmaster Tools.
• Immediate action: Treat the appearance of many unfamiliar IPs as a potential attack on your customers or brand reputation. Rapid investigation and mitigation are crucial.

Key opinions

• SaaS product usage: One common cause is someone within the company using a new SaaS product that uses your domain for email authentication, inadvertently adding its IPs to your sending reputation.
• Internal mail server moves: Changes to your company's internal mail servers can introduce new IP addresses that then appear in PMT data. This is similar to unexpected IP appearances on SenderScore for dedicated IPs.
• Forgotten SMTP connectors: The sudden volume from an overlooked or legacy SMTP connector can push its traffic over the PMT reporting threshold.
• AWS SES instances: Someone might have spun up an Amazon SES (Simple Email Service) instance to send transactional emails like password resets, without integrating it into the main email infrastructure oversight.
• Scale of problem: Discovering over 40 unfamiliar IP addresses indicates a widespread issue that requires immediate attention and comprehensive investigation.

Key considerations

• Verify internal operations: Conduct a thorough audit of all departments and services within your company to identify any new or existing applications sending emails under your domain that haven't been accounted for.
• PMT accuracy: While Postmaster Tools is generally accurate, it's worth considering the possibility of subtle reporting anomalies, though phantom IP addresses are rare. Generally, it's best to investigate.
• DMARC report access: Ensure you have full access to your DMARC reports, as these are the most reliable way to identify all IPs sending emails from your domain and their authentication status. This is crucial for managing senders during a blocklisting event.
• Immediate investigation: A large number of unfamiliar IP addresses appearing suddenly warrants an urgent, comprehensive investigation to prevent potential damage to your sender reputation or email deliverability. The Abusix blog further explains why an IP address might be flagged as suspicious.
• Internal team collaboration: Work closely with your IT and security teams. Their expertise in network traffic and system configurations can be invaluable in tracing the origin of these IPs.

Key opinions

• PMT accuracy vs. subtle anomalies: While Postmaster Tools typically provides accurate data, any 'lying' is usually subtle, like temporary domain reputation drops, not the appearance of completely phantom IPs. If an unexpected IP is there, it's likely sending mail.
• Hidden sending sources: A forgotten SMTP connector's volume could suddenly reach Google Postmaster Tools' reporting threshold, revealing a previously unnoticed sending source. This also applies if a bad IP reputation appears as a false positive.
• DNS inconsistencies: Discrepancies where forward DNS lookups don't match reverse DNS (PTR) records are strong indicators of suspicious activity, as legitimate senders usually maintain consistent DNS.
• Registrar connection: IPs associated with domains registered through your company's registrar but using email privacy services are highly suspect, especially if they also have inconsistent DNS.
• Snowshoe spam tactics: The appearance of many unfamiliar IPs with inconsistent DNS records and association with privacy services strongly suggests snowshoe domains or similar spamming tactics.
• Cybersecurity threat: The presence of such IPs, particularly in large numbers, could be part of a distributed attack against your customers or an attempt to leverage your domain's reputation for malicious purposes.

Key considerations

• DMARC report imperative: Access to and analysis of DMARC aggregate reports are non-negotiable for forensic analysis, allowing you to identify all IPs attempting to send mail as your domain.
• Security team collaboration: Immediately involve your corporate security teams to monitor outbound traffic from any identified suspicious IPs, as they may have advanced network monitoring tools.
• Abuse team expertise: Leverage the expertise of your abuse team. They are equipped with specialized tools and knowledge to handle incidents involving domain misuse or email blocklisting.
• DNS record validation: Rigorously investigate PTR records and their corresponding A records for all unfamiliar IPs to confirm legitimate setups or identify malicious ones. For more insights on how suspicious activity can affect your sender reputation, refer to this article from Abusix.
• RIR investigation: Trace the IPs through their Regional Internet Registry (RIR) to understand their allocation and identify if they belong to a known legitimate entity or a suspicious one.
• Proactive defense: Implement and maintain robust email authentication protocols such as DMARC, SPF, and DKIM to prevent domain spoofing and strengthen your sender identity against unauthorized usage.

Key findings

• PMT scope: Google Postmaster Tools aggregates data for all IP addresses that send email purporting to be from a domain, whether authorized or not, making it a critical monitoring tool.
• DMARC role: DMARC (Domain-based Message Authentication, Reporting & Conformance) is designed to provide domain owners with visibility into all sending sources and their authentication results, including those that fail.
• SPF mechanism: SPF (Sender Policy Framework) allows a domain to explicitly publish a list of authorized sending IPs. If an email originates from an IP not on this list, it should ideally fail SPF checks.
• DKIM signatures: DKIM (DomainKeys Identified Mail) uses cryptographic signatures to ensure that an email has not been tampered with in transit and was sent by an authorized sender.
• PTR records: Reverse DNS (PTR) records are essential for email sending reputation, as they link an IP address back to a hostname. Inconsistencies are a common indicator of spamming activity.

Key considerations

• Comprehensive DMARC implementation: Implement a DMARC policy, even a permissive one like p=none, to receive RUA (aggregate) reports. These reports are invaluable for uncovering all IPs sending as your domain.
• Regular DMARC report analysis: Consistently review DMARC aggregate reports to identify any unexpected sending IPs, authentication failures, or suspicious patterns that could indicate unauthorized activity. This helps you to better understand the Google Postmaster Tools spam rate dashboard.
• SPF record maintenance: Ensure your SPF record is always up-to-date, accurately listing all legitimate sending IPs and including all necessary third-party senders, such as include:spf.mail.com.
• Monitoring PMT daily: Frequent checks of Google Postmaster Tools are essential for early detection of any reputation changes or the sudden appearance of new IPs. For more information about suspicious IPs, see this article on IP listing.
• DNS hygiene: Verify that all legitimate sending IPs have correctly configured forward and reverse DNS entries to ensure proper email authentication and avoid reputation issues.