Why do legitimate emails sometimes trigger phishing warnings?

Gmail's machine learning algorithms are designed to identify patterns associated with phishing scams. Even if your email is legitimate, it might contain elements, such as deceptive links or suspicious phrasing, that resemble known phishing attempts. Your sender reputation and recipient engagement also play a significant role.

Does a phishing warning mean my email went to spam?

The warning indicates that Gmail's filters detected something suspicious. It's a cautionary flag for the recipient, but it doesn't always mean the email went to the spam folder. Often, the email is delivered to the inbox with the warning overlaid.

What common link issues cause Gmail phishing warnings?

The primary cause is often a mismatch between the visible link text and the actual URL. Other factors include using untrusted link shorteners or linking to compromised sites. It's crucial to ensure your links are transparent and lead to trusted domains.

Can removing alt tags from images cause phishing warnings?

No, removing alt tags from images is highly unlikely to cause phishing warnings. It's more of an accessibility best practice. The issue usually stems from more fundamental aspects like authentication, links, or content patterns.

How does user engagement affect sender reputation?

Your sender reputation is largely based on how recipients interact with your emails. If your subscribers consistently open, click, and reply to your emails, your reputation improves. Conversely, if they mark your emails as spam or delete them unread, your reputation declines, increasing the risk of warnings.

Why are my emails triggering Gmail phishing warnings and how can I fix it? - Troubleshooting - Email deliverability - Knowledge base

Seeing a This message seems dangerous warning in

Gmail can be quite alarming, especially when you know your emails are legitimate. It's frustrating to send out important communications only to have recipients see a security alert, even if the email isn't routed to the spam folder. This often indicates that Google's systems, despite their sophistication, perceive some element of your email as suspicious or characteristic of a phishing attempt.

These warnings are designed to protect users from malicious content, but sometimes, legitimate senders can inadvertently trigger them. It's a complex issue that goes beyond simple spam filtering and delves into how Google assesses the trustworthiness of an email, its sender, and its content. Resolving it requires a detailed look at various factors, from technical configurations to the specifics of your email's design and links.

How Gmail identifies phishing warnings

Google's email filtering systems are incredibly advanced, employing various signals to determine if an email is safe or suspicious. It's not just about what words you use, but also about the technical underpinnings of your email and the overall reputation of your sending domain. These signals collectively form an assessment of whether your email might be a phishing attempt or contain unsafe content.

A key aspect of this detection involves analyzing the sender's legitimacy. Google checks email authentication protocols like SPF, DKIM, and DMARC. If these are improperly configured or missing, it raises red flags, as legitimate senders typically have these in place to prevent spoofing. Furthermore, Gmail's security measures also scrutinize the content of the email itself, looking for patterns commonly associated with phishing scams, such as urgent calls to action or requests for sensitive personal information.

Crucially, Google's machine learning algorithms play a significant role. These algorithms learn from user feedback and detected threats to identify new phishing tactics. This means even if your email isn't overtly malicious, it might share characteristics with emails previously marked as phishing by other users, leading to a false positive. This is why some users might see the warning, while others don't, depending on their individual engagement history and Gmail's evolving threat intelligence. For more information on why Gmail flags messages as suspicious, check out our guide on why Gmail shows 'This message seems dangerous'.

Technical authentication and infrastructure

One of the most common reasons for phishing warnings relates to how your emails are authenticated. SPF, DKIM, and DMARC are crucial for proving that your emails are legitimately from your domain and haven't been tampered with. Without proper configuration, even benign emails can look suspicious to receiving mail servers, including Gmail's. These protocols help establish trust and are foundational for good deliverability. We have an in-depth guide on DMARC, SPF, and DKIM.

SPF (Sender Policy Framework): Specifies which mail servers are authorized to send emails on behalf of your domain. A missing or incorrect SPF record can lead to authentication failures.
DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, allowing recipients to verify that the email was not altered in transit.
DMARC (Domain-based Message Authentication, Reporting & Conformance): Builds on SPF and DKIM, telling receiving servers how to handle emails that fail authentication and providing reporting mechanisms.

It's also essential to ensure your email service provider (ESP) like

SendGrid is properly configured and has a good sending reputation. If your ESP's shared IPs or domains are associated with suspicious activity, it can negatively impact your deliverability, even if your own practices are sound. Regularly monitoring your domain reputation through Google Postmaster Tools is a crucial step.

Key authentication records

SPF: Add a TXT record to your DNS that lists authorized sending IP addresses and domains.
DKIM: Generate a public/private key pair and publish the public key as a DNS TXT record.
DMARC: Create a TXT record that specifies your policy for emails failing SPF or DKIM, and where to send reports.

Email content and link scrutiny

Beyond technical configurations, the content of your email and how you handle links are major culprits for phishing warnings. Gmail's filters are designed to spot deceptive practices. For example, if the visible text of a link (what the user sees) doesn't match the actual destination URL (where the link goes), it's a huge red flag. This is a classic phishing tactic, even if your intentions are legitimate. This is particularly true if you are linking to a login page.

This issue often arises with click-tracking services provided by ESPs like

SendGrid. While these services are standard for analytics, if the display text of your link shows one domain (e.g., yourdomain.com) but the actual href points to the tracking domain (e.g., ct.sendgrid.net), Gmail might interpret this as an attempt to deceive the user. This is a common pitfall that can trigger phishing alerts, even if your links are technically valid and safe.

Beyond misaligned links, other content-related issues can contribute. Using shortened links, especially generic ones not associated with your brand, can trigger warnings. Hidden content through HTML or CSS manipulations, common in deceptive emails, will also be flagged by Google. Even the general language and imagery, if it mimics known phishing campaigns or is overly generic, can contribute to the warning.

Bad link practice

Displaying the actual URL in the link text when it redirects through a different domain can appear deceptive. For example, if you show "yourdomain.com" but the actual link points to a tracking domain like ct.sendgrid.net, this will raise alarms. This is considered a very bad practice.

Deceptive link HTML exampleHTML

<a href="https://u5080173.ct.sendgrid.net/ls/click?upn=Am-2FwBjzRC=...">GROUPS.GOOGLE.COM</a>

Good link practice

Instead of using the bare hostname, use descriptive text for your links. For example, use "Click here for our latest blog post" or "Access your account." This avoids the mismatch between the visible text and the actual URL, which is a major factor in phishing detection.

Sender reputation and user engagement

Ultimately, a significant factor in Gmail's filtering decisions is your sender reputation, which is heavily influenced by user engagement. If your subscribers consistently open, read, reply to, and move your emails to their primary inbox, Google learns that your mail is wanted. Conversely, if emails are often deleted unread, marked as spam, or ignored, your reputation suffers, increasing the likelihood of warnings or direct spam placement. This is why Gmail flags messages as suspicious due to low sender reputation.

This also explains why deliverability testing tools might show inconsistent results. These tools use fresh, unengaged accounts, which don't have the positive engagement history that your actual subscribers might have. Therefore, a test email to a new account might land in spam or receive a warning, while the same email to an engaged subscriber goes directly to the inbox.

Maintaining a healthy sender reputation involves consistent engagement, sending relevant content, and regularly cleaning your email lists to remove inactive or unengaged subscribers. It's a long-term commitment that pays off in better inbox placement and fewer phishing warnings. You can learn more about this by reading our article Why Your Emails Are Going to Spam.

Improving sender reputation

Engage recipients: Encourage opens, clicks, replies, and adding your address to their contacts.
Clean your lists: Regularly remove inactive or unengaged subscribers to reduce bounces and spam complaints.
Monitor feedback: Use Google Postmaster Tools to track your spam rate and domain reputation.

Views from the trenches

Best practices

Ensure full transparency in link text, making sure what's visible matches the actual destination URL to avoid appearing deceptive.

Implement strong email authentication (SPF, DKIM, DMARC) consistently across all sending domains to build sender trust.

Prioritize user engagement by sending relevant, valuable content to active subscribers, which is critical for Gmail's filtering.

Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools to identify and address issues proactively.

Provide a clear and easily accessible unsubscribe option, like a List-Unsubscribe header, to allow users to opt-out gracefully rather than mark as spam.

Common pitfalls

Using a visible link text that doesn't match the hidden destination URL, even with legitimate click-tracking, can trigger phishing warnings.

Neglecting email authentication (SPF, DKIM, DMARC) or having misconfigured records signals untrustworthiness to Gmail.

Sending emails to unengaged or inactive subscribers can significantly harm your sender reputation and increase spam complaints.

Overly aggressive or suspicious language, combined with urgent calls to action, can cause legitimate emails to be flagged as phishing.

Removing critical HTML attributes like alt tags from images to save bytes can negatively impact email rendering and potentially signal poor quality.

Expert tips

If troubleshooting a new template, try isolating elements. Remove sections or types of links one by one to pinpoint the exact trigger for the warning.

Understand that testing tools with 'probe' accounts may not accurately reflect real-world inbox placement due to Gmail's engagement-based filtering.

Focus on the long-term relationship with your subscribers; their positive interactions are the strongest signal of legitimacy to Gmail.

Be cautious with generic link shorteners; if using an ESP's tracking, ensure your custom tracking domain is well-reputed.

Always include a plain-text version of your email. It's a foundational best practice that can contribute positively to deliverability.

Expert view

Expert from Email Geeks says that without the actual email template, it is difficult to identify the exact cause, but common issues include external links to poor-quality hosting, stealth redirects, attachments, bad HTML, or content copied from phishing campaigns.

2020-02-04 - Email Geeks

Expert view

Expert from Email Geeks says that the first things to investigate are the URLs in the links and domain authentication. Removing alt tags from images is unlikely to cause such an issue.

2020-02-04 - Email Geeks

Summary of solutions

Dealing with Gmail phishing warnings requires a multi-faceted approach. It's rarely one single issue but rather a combination of factors related to your technical setup, email content, and sender reputation. The first step is always to ensure your email authentication (SPF, DKIM, DMARC) is impeccable, as this builds fundamental trust with mailbox providers. Remember that recognizing and avoiding phishing scams yourself helps you create emails that don't inadvertently mimic them.

Next, pay close attention to your email content, particularly how links are displayed. Avoid any discrepancy between visible link text and the actual URL. Finally, prioritize fostering strong user engagement, as your subscribers' interactions with your emails are Gmail's strongest signal of your legitimacy. By addressing these areas comprehensively, you can significantly reduce the incidence of phishing warnings and improve your overall email deliverability. For more guidance, explore our resource on how to troubleshoot Gmail phishing email warnings.