Why do emails get a phishing warning in Gmail and how to prevent it?
Michael Ko
Co-founder & CEO, Suped
Published 6 Aug 2025
Updated 19 Aug 2025
6 min read
Seeing a phishing warning in Gmail for your legitimate emails can be incredibly frustrating. It directly impacts your deliverability and trustworthiness with recipients, leading to reduced open rates and engagement. When your carefully crafted message lands with a red banner, it undermines all your efforts.
I've seen this happen to many senders, where valid communications are mistakenly flagged. It’s a common misconception that these warnings are solely due to an email being classified as spam. While spam filters play a role, phishing warnings are a distinct category, often triggered by more sophisticated detection mechanisms that look beyond typical unsolicited bulk email characteristics.
This guide will explore the primary reasons Google flags emails as potential phishing attempts, even when they're not. More importantly, I'll provide actionable steps you can take to prevent these warnings and ensure your emails reach the inbox safely and effectively.
Why Gmail flags emails as phishing
Gmail employs sophisticated algorithms to identify phishing attempts. These systems analyze various factors beyond simple spam keywords or generic content. They look for patterns that mimic malicious emails, such as requests for sensitive information (e.g., passwords or financial details), even if your email's intent is benign.
A key differentiator is that phishing warnings are often triggered by context rather than just content. For example, mismatched domains in links or a history of an IP address hosting phishing sites can lead to a flag. This is why a legitimate email might still receive a dangerous message alert.
These warnings are not the same as being caught by a general spam filter or placed on a blacklist (or blocklist). While a sender might be listed on a blocklist, a phishing warning from Gmail specifically indicates a perceived security threat. It's a much more dynamic detection that often involves real-time analysis of links and domain reputation.
Common technical triggers and how to fix them
Several technical misconfigurations or practices can inadvertently trigger phishing warnings. Proper email authentication is foundational. If your SPF, DKIM, and DMARC records are not correctly set up or aligned, Gmail may view your emails as suspicious because it cannot verify their authenticity.
Another common culprit is using shared IP addresses or shared infrastructure, especially free or public URL shorteners. If someone else using the same shared IP or service engages in malicious activity, it can negatively impact your sender reputation, even if your practices are legitimate. This is a significant factor in inconsistent suspicious link warnings.
Content-wise, emails that attempt to mimic security alerts or critical notifications, especially those prompting immediate action or asking for login credentials, are red flags. Even if your intention is to provide a legitimate login link, Gmail's filters are designed to be overly cautious regarding sensitive actions.
I often advise senders to follow Google's advice on avoiding phishing to ensure their emails comply with Gmail's internal security checks. This often includes scrutinizing how you embed links, especially those leading to login pages or external services.
Content and sender reputation best practices
To prevent these frustrating warnings, you need a multi-faceted approach focusing on technical configurations and content best practices. Here are some key strategies:
Strengthen Authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. This is the first line of defense against spoofing and impersonation, which phishing attempts rely on.
Avoid Public URL Shorteners: Services like Bit.ly and Goo.gl are often abused by phishers. Using them can automatically trigger warnings, as Gmail might perceive such links as attempts to mask a malicious destination. If you need to shorten links, use your own domain or a private tracking domain provided by your Email Service Provider (ESP).
Monitor Shared IP Reputation: If you're on a shared IP, ensure your ESP actively manages their reputation and prevents abusive senders. Tools like a blocklist checker can give you some insight, but Gmail's internal systems are the most important. If issues persist, consider a dedicated IP if volume justifies it.
Even with perfect technical setup, problematic content can still trigger warnings. Gmail prioritizes user safety, so any content resembling phishing lures will be flagged. This includes deceptive subject lines, urgent calls to action, or suspicious-looking links, even if they're not malicious.
Content to avoid
Generic Greetings: Emails starting with Dear customer or similar phrases, especially from transactional senders.
Urgency and Threats: Phrases like Your account will be suspended or Immediate action required.
Mismatched Domains: Links that display one domain (e.g., your legitimate site) but lead to another (e.g., a tracking domain that resolves to a suspicious IP).
Content to embrace
Personalization: Use recipient's name in greetings to signify legitimacy.
Clear Call to Actions: Be direct and transparent about what you want recipients to do.
Maintaining a healthy sender reputation is paramount. Gmail (and other Mailbox Providers) closely monitors how recipients interact with your emails. High engagement rates, low spam complaints, and minimal bounces contribute to a positive reputation. Conversely, if users frequently mark your emails as spam, or if your bounce rates are high, your sender reputation will suffer, increasing the likelihood of phishing warnings. Learn more about how sender reputation affects warnings.
Maintaining deliverability in a vigilant inbox landscape
Navigating Gmail's sophisticated phishing detection systems requires vigilance and a deep understanding of email deliverability best practices. It’s not just about avoiding traditional spam triggers, but also about building trust through consistent, authenticated, and user-friendly email experiences. By addressing the technical and content-related factors discussed, you can significantly reduce the chances of your emails being flagged.
Remember, proactive monitoring of your email deliverability metrics and regular checks of your domain's reputation are crucial. Staying informed about changes in mailbox provider policies, like those from Google and Yahoo, will also help you maintain excellent deliverability and avoid unwelcome phishing warnings.
Views from the trenches
Best practices
Always ensure your domain's SPF, DKIM, and DMARC records are correctly configured and aligned for all sending sources.
Use dedicated sending IPs if your email volume and budget allow, to avoid reputation issues from other senders.
Regularly audit all links in your emails to ensure they point to legitimate, well-reputed domains, ideally your own.
Educate your team on email content best practices, especially concerning sensitive information requests or urgent calls to action.
Monitor your sender reputation using tools like Google Postmaster Tools for Gmail-specific insights.
Common pitfalls
Relying on public URL shorteners (e.g., bit.ly, goo.gl) which are often associated with malicious activities.
Ignoring mixed domain usage in emails where display URLs differ significantly from actual linked URLs.
Assuming a blacklist listing is the sole cause of a phishing warning when it's often a sign of deeper underlying issues.
Sending emails with generic 'Dear customer' greetings or overly urgent language that mimics phishing scams.
Not having strong email authentication, leading to Gmail perceiving your emails as unverified or spoofed.
Expert tips
Investigate mismatched domains between the email's 'From' address and the domains in your email body and links.
Be wary of any shared infrastructure (IPs or link tracking domains) if it has a history of hosting compromised sites.
Implement custom tracking domains from your ESP to prevent your main domain's reputation from being tied to third-party services.
If troubleshooting a warning, first check for inconsistencies in link destinations and sender identity, then review content for phishing heuristics.
Understand that a 'phishing warning' is distinct from a 'spam warning' and requires a different investigative approach.
Marketer view
Marketer from Email Geeks says they have seen phishing warnings in emails that ended up in their spam folder.
2023-03-21 - Email Geeks
Expert view
Expert from Email Geeks says that a phishing warning indicates something bad in the message itself, or that it is hosted on an IP associated with phishing sites.
Gmail for your legitimate emails can be incredibly frustrating. It directly impacts your deliverability and trustworthiness with recipients, leading to reduced open rates and engagement. When your carefully crafted message lands with a red banner, it undermines all your efforts.
Google flags emails as potential phishing attempts, even when they're not. More importantly, I'll provide actionable steps you can take to prevent these warnings and ensure your emails reach the inbox safely and effectively.
Bit.ly and 
Goo.gl are often abused by phishers. Using them can automatically trigger warnings, as Gmail might perceive such links as attempts to mask a malicious destination. If you need to shorten links, use your own domain or a private tracking domain provided by your Email Service Provider (ESP).
emails visually align with your brand's website.
Yahoo, will also help you maintain excellent deliverability and avoid unwelcome phishing warnings.
