Why are Gmail emails flagged with 'Images are hidden, this message might be suspicious' banner?
Michael Ko
Co-founder & CEO, Suped
Published 29 Jul 2025
Updated 17 Aug 2025
7 min read
Seeing the banner "Images in this message are hidden. This message might be suspicious or spam" in Gmail can be quite unsettling for any sender. It implies that your message, despite potentially being legitimate, is perceived as a threat. This warning actively discourages recipients from interacting with your email, potentially impacting open rates, click-through rates, and overall engagement.
The primary purpose of such banners is to protect users from phishing attempts, malware, and unwanted spam. Gmail's advanced filtering systems, which utilize machine learning, analyze various signals to determine the trustworthiness of an incoming email. When these systems detect anomalies or indicators of potential risk, they err on the side of caution by displaying a warning.
It's important to understand that this banner isn't just about images. While it explicitly mentions images being hidden, the underlying cause is often a broader issue with the email's perceived legitimacy, rather than a specific problem with the image files themselves. The hidden images are a symptom, not the root cause.
In this guide, I'll explore the common reasons behind this Gmail warning and provide actionable steps to help ensure your emails land in the inbox without triggering suspicious flags.
Sender reputation and authentication
The most frequent culprit behind the "Images are hidden, this message might be suspicious" banner is a low sender reputation. Gmail assigns a reputation score to every sender based on a multitude of factors, including past sending behavior, spam complaint rates, and engagement metrics. If your reputation is low or has recently declined, Gmail is more likely to view your emails with suspicion.
A key component of sender reputation is email authentication. Proper configuration of SPF, DKIM, and DMARC records is crucial for proving to recipient servers that your emails are legitimate and haven't been tampered with. Missing or misconfigured records can significantly harm your standing.
Furthermore, being listed on email blocklists (or blacklists) will severely damage your sender reputation. These lists compile IP addresses and domains associated with sending spam or malicious content. Even if your current email isn't spam, a historical presence on a blocklist can trigger warnings and prevent images from displaying. It's important to monitor blocklist monitoring regularly.
Low reputation factors
High complaint rates: If recipients frequently mark your emails as spam, it signals to Google that your content is unwanted. This can be tracked using Google Postmaster Tools.
Poor engagement: Low open rates and click rates, coupled with high deletion rates without opening, can indicate disinterest or suspicion from recipients.
Sending to invalid addresses: A high bounce rate suggests poor list hygiene, which negatively impacts your reputation.
Suspicious content and linking practices
Gmail's filters also scrutinize the content of your emails for suspicious elements. While images themselves aren't inherently malicious, how they are hosted and linked can trigger warnings. For instance, images hosted on domains with poor reputations or on shared generic CDNs (content delivery networks) might be flagged.
One common issue is the use of image-based tracking pixels. While these are standard in email marketing to measure opens, Gmail may perceive them as suspicious, especially from senders with a nascent or poor reputation. Google's machine learning algorithms are designed to detect such hidden elements, especially if they lead to untrusted domains, as part of their advanced phishing and malware protection.
Content that mimics phishing attempts or contains suspicious links will also trigger these banners. This includes emails with generic greetings, unusual grammar, or links that redirect to unexpected or unverified domains. Even if your intentions are benign, characteristics commonly associated with spam or malicious content can result in your images being hidden and a warning being displayed. Learn more about why emails get phishing warnings.
Recipient engagement and list hygiene
User interaction (or lack thereof) plays a significant role in Gmail's assessment of your emails. If recipients consistently ignore, delete without opening, or worse, mark your emails as spam, Gmail's filters learn that your messages are undesirable. This negative feedback loop can lead to the "Images are hidden" banner, even for otherwise compliant emails.
Conversely, positive engagement, such as opening, clicking links, replying, or adding your address to contacts, reinforces a positive sender reputation. Gmail uses this data to refine its filtering decisions for each individual user and the broader email ecosystem.
Furthermore, if your email list contains a high percentage of inactive or disengaged users, or if you're sending to spam traps, your reputation will suffer. This directly influences Gmail's willingness to display images or even deliver your emails to the inbox. It's a critical reason why your emails might go to spam.
Resolving the banner: actionable steps
Addressing the "Images are hidden" banner requires a multi-faceted approach, focusing on improving your overall email deliverability. The first step is to ensure your authentication records are impeccable. Use a DMARC record generator to set up a robust policy for your domain, helping mitigate spoofing and phishing attempts that could tarnish your reputation.
Next, focus on content and infrastructure. Make sure your images are hosted on a reputable CDN with a strong domain reputation. If you're using a third-party email service provider, ensure their infrastructure is also in good standing. Avoid using excessively large images or emails that are entirely image-based, as these can look suspicious to spam filters. Also, review all links within your email to ensure they are secure (HTTPS) and lead to trusted, branded domains.
Finally, prioritize recipient engagement and list hygiene. Regularly clean your email lists to remove inactive or invalid addresses, and implement double opt-in processes to ensure genuine interest from new subscribers. Encourage recipients to add your address to their contacts and to mark your emails as "not spam" if they accidentally land in the junk folder. Consistent positive engagement will naturally improve your sender reputation and reduce the likelihood of these warnings.
Technical checks
Ensure your domain's SPF, DKIM, and DMARC records are correctly configured. DMARC monitoring helps you track authentication failures.
Verify that your image hosting domain and all linked URLs have a good reputation. Branded domains are preferable.
Content & audience strategy
Avoid suspicious phrasing or overly promotional language that might trigger spam filters. Focus on clear, valuable content.
Regularly clean your email lists to remove inactive subscribers, reducing bounce and complaint rates.
Views from the trenches
Best practices
Always ensure email authentication (SPF, DKIM, DMARC) is correctly set up and monitored for your sending domains.
Host images on a dedicated subdomain of your primary sending domain to consolidate reputation and avoid generic CDN issues.
Segment your audience and send relevant content to minimize spam complaints and maximize positive engagement metrics.
Regularly clean email lists to remove inactive subscribers and potential spam traps, maintaining a healthy list.
Review your email content for anything that might appear suspicious, like overly promotional language or unusual formatting.
Common pitfalls
Failing to implement DMARC with an enforcement policy can leave your domain vulnerable to spoofing and reputation damage.
Using shared or generic image hosting services (like public cloud storage) can lead to reputation issues if others abuse them.
Ignoring low engagement rates or high spam complaint rates in Google Postmaster Tools, which indicates a problem.
Sending emails to old, unengaged, or purchased lists, which often contain invalid addresses and spam traps.
Over-reliance on image-only emails or large images that are difficult for spam filters to analyze.
Expert tips
Monitor email engagement metrics closely, as consistent low engagement can signal to Gmail that your content is not valued.
Consider warming up new sending IPs or domains gradually to build a positive reputation with mailbox providers.
If using a third-party email service provider, understand their reputation and how it impacts your deliverability.
Regularly check your domain and IP on common blocklists (blacklists) to ensure you haven't been listed.
Conduct A/B tests on email content and subject lines to identify what resonates best with your audience and improves engagement.
Expert view
Expert from Email Geeks says they have observed this banner appearing more frequently in recent weeks, indicating it might be a new trend, though not yet widespread.
2024-08-19 - Email Geeks
Expert view
Expert from Email Geeks suggests checking the reputation of image URLs or CDNs used in the email, as problematic image hosting could be a contributing factor.
2024-08-19 - Email Geeks
Restoring trust in your emails
The "Images are hidden, this message might be suspicious" banner in Gmail is a clear signal that your email's trustworthiness is under scrutiny. It's rarely a simple issue with images alone; instead, it points to deeper concerns regarding your sender reputation, email authentication, content quality, and recipient engagement.
By proactively addressing these areas, you can significantly improve your email deliverability and ensure your messages are displayed as intended. Prioritize strong authentication, maintain a clean sending list, craft engaging content, and monitor your sender reputation closely. Doing so will not only remove the suspicious banner but also foster stronger trust with your audience and improve your overall email program.
Gmail can be quite unsettling for any sender. It implies that your message, despite potentially being legitimate, is perceived as a threat. This warning actively discourages recipients from interacting with your email, potentially impacting open rates, click-through rates, and overall engagement.
Google that your content is unwanted. This can be tracked using Google Postmaster Tools.
