Why do emails get a phishing warning in Gmail and how to prevent it?

Key findings

• Phishing vs. spam: Gmail's phishing warnings are different from spam classifications and signal that the email is perceived as trying to trick recipients into revealing sensitive information.
• Content analysis: Warnings often arise from suspicious content patterns, such as mismatched domains in visible text versus hyperlinks (HREFs), or words commonly associated with scams like 'free'.
• Associated IPs and domains: An email might be flagged if its sending IP address, or any domains it links to, are known to host or have been associated with phishing sites.
• Shared infrastructure risk: Using shared IPs or public URL shorteners can expose your emails to reputation issues stemming from other users' malicious activities, even if your content is legitimate.

Key considerations

• Authentication: Ensure your email authentication records (SPF, DKIM, DMARC) are correctly configured to prove sender legitimacy and prevent spoofing.
• Link hygiene: Always use clean, direct URLs that link primarily to your own content. Avoid public URL shorteners like Goo.gl or Bit.ly, as they are frequently abused by phishers.
• Domain reputation monitoring: Regularly check your domain and any linked domains for blacklisting or security flags, although direct blacklist listings may not be the primary cause of phishing warnings.
• Understand phishing tactics: Educate yourself and your team on common phishing indicators and social engineering techniques to prevent accidental mimicry in legitimate campaigns. The FTC offers valuable resources on how to recognize and avoid phishing scams.

Key opinions

• Initial confusion: Many marketers initially mistake phishing warnings for generic spam detections, leading them to check their sender IP on common blacklists, which often yields irrelevant results for phishing-specific issues.
• Shared IP concerns: Marketers on shared IP addresses often worry that other users' problematic behavior might be negatively affecting their own email deliverability and triggering phishing alerts.
• Content flags: Some marketers speculate that specific words in subject lines, such as 'free,' could be contributing to phishing warnings, though this is often not the primary cause for such severe flags.
• Link tracking impact: There is concern about how link tracking might contribute to phishing warnings, especially if not handled properly, although direct causation is not always clear.

Key considerations

• Beyond blocklists: While checking blocklists (or blacklists) is a common first step, understand that Gmail's phishing warnings typically stem from more nuanced factors like content analysis, sender reputation, and associated domains rather than simple IP listings. Learn more about how email blacklists actually work.
• Holistic deliverability checks: Focus on a comprehensive deliverability audit that includes examining email headers, sender authentication, link destinations, and the overall context of your message. This approach helps in diagnosing email deliverability issues.
• Proactive prevention: Actively work to prevent your domain from being marked unsafe. Cybersecurity experts often advise to be vigilant about unsolicited links and verify sender authenticity to avoid phishing scams.

Key opinions

• Phishing vs. spam distinction: Experts strongly emphasize that Gmail's phishing warnings are distinct from spam classifications, focusing on deceptive intent rather than just unwanted bulk mail.
• Dynamic detection: Phishing detection is highly dynamic, often reacting to compromised hosts or specific heuristics related to deceptive practices.
• Link and domain scrutiny: Gmail scrutinizes mismatched domains in HREFs and visible text, as well as domains or IPs linked in the email that are associated with known phishing sites.
• Blocklist relevance: Many blacklists (or blocklists) have little to no direct impact on phishing warnings; very few actually affect delivery for such alerts.
• Shared infrastructure caution: Using shared infrastructure, particularly free public URL shorteners, significantly increases the risk of being flagged due to the actions of other users.

Key considerations

• Focus on content and links: Prioritize auditing your email content and all included links for consistency and reputation. Ensure that all linked domains are legitimate and not compromised. This is key to resolving a low Gmail domain reputation.
• Infrastructure choice: If possible, avoid shared infrastructure, especially free public services, to minimize exposure to others' poor sending practices. When using an ESP, ensure they actively police their users.
• Leverage security tools: Utilize public data APIs and tools like VirusTotal to check domains and URLs for phishing or malware associations, though manual checks are rarely sufficient for broad issues. A thorough understanding of your email domain reputation is essential.
• Monitor bounce logs: While phishing warnings might not always result in bounces, your bounce logs can provide insights into other deliverability issues that may indirectly contribute to a flagging of your messages.

Key findings

• Automatic protection: Gmail's phishing and malware protections are automatically enabled by default, indicating a proactive approach to user security.
• Behavioral analysis: Warnings are triggered when systems detect behaviors or characteristics commonly associated with scam attempts, such as requests for personal information or unusual reply-to addresses.
• Domain and link verification: Security systems often check if links within an email redirect to suspicious sites or if the sender's domain has a history of malicious activity.
• User interaction flags: Alerts may appear when a user is about to reply to an address not in their contact list or company domain, as a preventative measure against impersonation.

Key considerations

• Adhere to sender guidelines: Follow best practices for bulk senders, which include strong email authentication (SPF, DKIM, DMARC) and maintaining a good sender reputation. Google provides recommendations on how Gmail helps users avoid email scams.
• Monitor with postmaster tools: Utilize tools like Google Postmaster Tools to monitor your domain's reputation, spam rate, and delivery errors, which can indirectly signal potential issues leading to phishing warnings. Learn more about the ultimate guide to Google Postmaster Tools V2.
• Content best practices: Design emails to be clear, transparent, and avoid any elements that might inadvertently mimic phishing attempts. This includes ensuring consistent branding and legitimate link destinations.
• Understand warning variations: Recognize that Gmail displays various warning types based on its assessment of the threat. These banners are part of a robust defense system that aims to protect users from potential misuse of email addresses.