Why is Gmail throwing errors and marking my emails as phishing?

Key findings

• Private lists: Gmail maintains its own private blocklist of suspicious URLs, independent of public DNSBLs like Spamhaus.
• Compromised links: Phishing warnings often indicate a compromised website or brand domain hosting a phishing page, not necessarily an issue with the sender's email practices.
• Multiple ISP flags: If multiple Internet Service Providers (ISPs) flag a message as phishing, it strongly suggests a real security issue with the linked content.
• SPF limitations: While SPF records are crucial for authentication, SPF alone may not resolve phishing flags if the underlying linked content is deemed malicious.

Key considerations

• Investigate links: Always investigate linked URLs if emails are flagged as phishing, as a compromised site can affect your entire brand's email reputation.
• Beyond public lists: Understand that Gmail's internal algorithms go beyond standard DNSBL checks for identifying suspicious content.
• Strengthen authentication: Implement a strong DMARC policy alongside SPF and DKIM to bolster your email authentication and demonstrate legitimate sending.
• Monitor domain health: Regularly monitor your domain's health and look for any unauthorized content or pages hosted under your brand. For further assistance, refer to our guide on how to fix Gmail phishing warnings.

Key opinions

• Unlisted links: Some marketers observe that Gmail flags emails for suspicious links even if those links are not listed on common DNSBLs (DNS-based blocklists).
• False positives: A common concern is legitimate link tracking URLs being mistakenly identified as phishing, leading to a 'be careful with this message' warning.
• Internal mechanisms: Marketers suspect that Gmail has its own internal mechanisms for identifying bad URLs that are not publicly accessible.
• Site compromise: There is a shared understanding that a compromised site or hosting environment can directly impact email deliverability, leading to phishing warnings.

Key considerations

• Beyond public blocklists: Marketers should not solely rely on public blacklist checks (see our guide on email blocklists) when diagnosing Gmail phishing warnings.
• Secure assets: Prioritize securing all linked assets and subdomains to prevent their misuse for phishing purposes.
• Content focus: When a phishing warning appears, consider that the problem might be with the content (especially links) rather than just the sending infrastructure.
• Reputation impact: Address potential compromises on linked domains, as low sender reputation can lead to these warnings.

Key opinions

• Proprietary lists: Experts confirm that Google maintains its own private list of malicious URLs, which are distinct from public DNSBLs.
• Real compromise: They strongly suggest that if multiple ISPs are issuing phishing warnings, it's a clear indicator of actual phishing activity originating from or linked to the brand's assets.
• Underlying cause: The root cause of phishing warnings is often a compromised page on the brand's website or an associated domain being used for malicious purposes.
• SPF and Spamhaus: SPF records, while essential for authentication, are generally not the sole solution for resolving phishing flags related to suspicious content or compromised sites, and Spamhaus typically does not list domains for a lack of SPF.

Key considerations

• Phishing site removal: Focus efforts on identifying and removing any compromised pages or phishing content hosted on your brand's domain or linked subdomains.
• Advanced filters: Understand that Gmail's filters are highly advanced and aim to protect users from sophisticated threats, even if it occasionally flags legitimate content.
• Comprehensive authentication: Ensure all aspects of your email infrastructure, including third-party tracking domains, are secure and properly configured. For more details on maintaining your reputation with Gmail, consult our guide on improving domain reputation using Google Postmaster Tools.
• Blocklist nuances: Do not assume a lack of public blacklist listing means your links are safe from Gmail's scrutiny. Refer to resources like Mailgun's guide on preventing Gmail blocking for more insights.

Key findings

• Warning types: Gmail often displays warnings like "Be Careful With This Message" or marks emails as spam if it suspects misuse of an email address or the presence of suspicious content.
• Authentication gaps: Missing essential DNS records (like SPF and DKIM) or misaligned DKIM signatures can lead to messages being flagged as suspicious, even if they are legitimate.
• Spam rate impact: Violation of Gmail's bulk sender guidelines, including maintaining a high spam rate (above the acceptable limit of 0.3%), can result in emails being marked as spam or blocked.
• Comprehensive analysis: Gmail's filters analyze various factors, including sender reputation, content, and link reputation, to determine if an email poses a phishing risk.

Key considerations

• Proper authentication: Ensure your domain has proper SPF, DKIM, and DMARC authentication records configured and aligned.
• Monitor spam rates: Proactively monitor your spam rate (e.g., via Google Postmaster Tools) and address any increases promptly, as discussed in our article why your emails are going to spam.
• Content review: Regularly review email content for anything that might appear suspicious, such as generic login prompts or unusual links.
• Adhere to guidelines: Adhere strictly to Gmail's bulk sender guidelines to maintain a good sender reputation and avoid deliverability issues. For detailed insights on warnings, refer to UW-IT's guide on phishing and spam email. Also, check out why Gmail shows 'This message seems dangerous' warning.