Why are my emails triggering Gmail phishing warnings and how can I fix it?
Matthew Whittaker
Co-founder & CTO, Suped
Published 13 Jul 2025
Updated 13 Oct 2025
6 min read
Receiving a Gmail phishing warning for your legitimate emails can be incredibly frustrating. It means your carefully crafted messages are being flagged as suspicious, potentially harming your brand's reputation and significantly impacting your email deliverability. This isn't just about landing in the spam folder, it's about a stark warning message that can deter recipients from opening your emails entirely. Many factors contribute to these warnings, from technical misconfigurations to the content of your message itself.
When users see a warning like “Be careful with this message” or “This message seems dangerous,” it signals a serious trust issue. My experience has shown that these warnings often stem from a combination of authentication failures, deceptive content practices, or a poor sender reputation. Let's dive into the common reasons behind these flags and, more importantly, how you can address them to ensure your emails reach the inbox safely.
Authentication failures and domain credibility
Email authentication protocols like SPF, DKIM, and DMARC are fundamental to email security and deliverability. If these records are incorrectly configured or missing, Gmail's filters are more likely to view your emails with suspicion, leading to phishing warnings. These protocols verify that an email truly originates from the claimed sender and has not been tampered with in transit.
A misconfigured SPF record, a broken DKIM signature, or an absent DMARC policy can all weaken your domain's credibility. Gmail relies heavily on these signals to prevent spoofing and phishing attacks. When your email fails these checks, even if it's legitimate, it can be flagged as a potential threat. It's crucial to have a comprehensive understanding of DMARC, SPF, and DKIM for robust email security.
To prevent this, regularly audit your DNS records. Ensure that your SPF record includes all authorized sending sources, your DKIM keys are valid and properly configured, and your DMARC policy is set up correctly and enforced, ideally with a policy of p=quarantine or p=reject. Monitoring your DMARC reports is essential to catch any authentication failures. Our DMARC monitoring platform can provide the visibility you need to diagnose and fix these issues.
Deceptive content and suspicious links
Even with perfect authentication, your emails can trigger phishing warnings if their content or link structure appears deceptive. This is a common pitfall, especially with marketing or transactional emails that use tracking links. A significant red flag for Gmail is when the visible text of a link does not match the actual destination URL, or if the linked domain has a poor reputation.
Bad practice: deceptive links
When the visible text of a hyperlink shows one domain, but the underlying href points to a different one, Gmail's algorithms will flag this as suspicious. This is a classic phishing tactic. Even if you're using a legitimate email service provider (ESP) with click tracking, you need to be mindful of how these URLs are displayed.
Ensure that the visible text of your links accurately reflects their destination, or use generic, non-domain-specific text. This builds trust and avoids triggering automated phishing detectors. If using click tracking, ensure the tracking domain is either aligned with your brand or the visible text is generic.
Beyond misleading links, other content issues can also contribute. Hiding content using HTML and CSS, including suspicious attachments, or using images without alt attributes can all be interpreted as deceptive practices by spam filters. Furthermore, linking to domains or websites that have been compromised or are known for malicious activities (often referred to as blocklists or blacklists) will almost certainly result in a phishing warning. Regular security audits of your linked domains are essential.
Sender reputation and user engagement
Gmail's filtering system is highly sophisticated, with a strong emphasis on sender reputation and user engagement. Even if your emails pass all authentication checks and contain no deceptive links, a poor sender reputation can still lead to phishing warnings or placement in the spam folder. Your reputation is built on how recipients interact with your emails.
Factors like high unsubscribe rates, low open rates, frequent spam complaints, and a lack of positive interactions (like replies or forwards) can signal to Gmail that your emails are unwanted. This can damage your domain reputation over time. It's not just about avoiding bad practices, but actively fostering good engagement. If Gmail perceives that your subscribers don't want your mail, it will treat it accordingly, even if it's not technically malicious. Monitoring your Google Postmaster Tools dashboards is a key step.
Improving sender reputation
Maintain a clean email list: Regularly remove inactive or unengaged subscribers to reduce bounces and spam complaints.
Encourage positive engagement: Send relevant content that your subscribers genuinely want to open and interact with.
Monitor feedback loops: Pay attention to spam complaint data from Postmaster Tools and ESPs.
Implement List-Unsubscribe headers: Make it easy for recipients to unsubscribe rather than marking as spam.
Troubleshooting and monitoring your emails
Troubleshooting phishing warnings requires a systematic approach. Start by checking all your authentication records, then meticulously review your email content for any potentially deceptive elements, especially links. It's a process of elimination that can sometimes feel like finding a needle in a haystack.
Review DNS records: Double-check your SPF, DKIM, and DMARC entries. Ensure they are correctly published and aligned with your sending domains.
Inspect email content and links: Look for any discrepancies between visible link text and actual destinations. Remove any suspicious links or attachments.
Check sender reputation: Use Google Postmaster Tools to monitor your domain and IP reputation. Look for spikes in spam complaints or authentication failures. This is crucial for understanding why Gmail flags messages as suspicious.
If you are consistently seeing phishing warnings, especially for a new email template or campaign, try sending simplified versions to test accounts. Remove elements one by one to identify the trigger. Pay particular attention to how Gmail handles your messages, as documented in their help articles on phishing. Remember that different recipients might see different results based on their past engagement with your domain, making personal testing accounts less reliable than aggregate data.
Views from the trenches
Best practices
Always align your link's visible text with its destination URL, especially when using click tracking services.
Regularly monitor your domain's authentication health (SPF, DKIM, DMARC) through DMARC reports.
Prioritize sending relevant content to engaged subscribers to maintain a strong sender reputation with Gmail.
Ensure all images in your emails have proper alt attributes for accessibility and deliverability trust.
Common pitfalls
Failing to configure DMARC, SPF, and DKIM properly, leading to authentication failures and distrust.
Using deceptive links where the display text hides the true destination, a common phishing indicator.
Ignoring low engagement rates or high spam complaints, which degrade sender reputation over time.
Linking to domains with a poor reputation or compromised hosts, triggering immediate red flags.
Expert tips
Use a tool like Suped for DMARC reporting to gain insights into authentication failures quickly.
When troubleshooting, isolate potential issues by simplifying your email content and link structure.
Focus on user engagement metrics as Gmail heavily weighs how recipients interact with your mail.
Be patient, as reputation changes and filter adjustments can take a few days to propagate.
Marketer view
Marketer from Email Geeks says: An email's content and link structure are major factors in phishing classifications. If your HTML or links are poorly constructed or lead to bad hosts, Gmail will flag them.
2020-02-04 - Email Geeks
Expert view
Expert from Email Geeks says: Using hostnames in the visible text of a link that point to a different hostname in the 'a href' will cause phishing warnings and should never be done.
2020-02-06 - Email Geeks
Ensuring long-term email trust
Dealing with Gmail phishing warnings can be challenging, but understanding the underlying causes is the first step towards a solution. By focusing on robust email authentication, maintaining transparent and honest email content, and consistently nurturing a strong sender reputation through positive user engagement, you can significantly reduce the likelihood of your legitimate emails being flagged.
Remember, email deliverability is an ongoing effort that requires continuous monitoring and adaptation. Tools that provide clear visibility into your authentication status and DMARC reports are invaluable. By taking proactive measures and staying informed about best practices, you can build lasting trust with Gmail and ensure your messages consistently reach their intended audience.
