Summary
Gmail flags emails with the 'Images are hidden, this message might be suspicious' banner due to a combination of factors including authentication problems, poor sender reputation, content issues, and Gmail's own filtering mechanisms. Specifically, issues with SPF, DKIM, and DMARC configuration, high bounce rates, spam complaints, use of suspicious URLs, inconsistent sending IP addresses, spam-like content, broken image links, and poor list hygiene can all trigger the banner. Additionally, Gmail may be testing new UI elements or filtering algorithms, and welcome emails might be treated differently. User-specific safety and privacy settings can also contribute to emails being flagged.
Key findings
- Authentication Issues: Incorrect SPF, DKIM, and DMARC configurations significantly impact deliverability.
- Poor Sender Reputation: High bounce rates, spam complaints, and blacklisting negatively affect sender reputation.
- Content Problems: Suspicious URLs, spam-like keywords, and misleading subject lines trigger flagging.
- Image and URL Reputation: Broken image links, image CDNs and short or suspicious URLs impact deliverability.
- List Hygiene Impact: Outdated or invalid email addresses lead to high bounce rates and damaged reputation.
- Gmail Filtering: Gmail's filtering algorithms and UI experiments may contribute to the banner.
- Welcome Email Treatment: Welcome emails are potentially subject to stricter filtering rules.
- User Settings: Users safety or privacy settings may cause the banner to appear.
Key considerations
- Implement Correct Authentication: Ensure SPF, DKIM, and DMARC records are properly configured.
- Maintain Sender Reputation: Monitor sender reputation and take steps to address issues like high bounce rates or spam complaints.
- Optimize Email Content: Avoid using spam-like keywords, suspicious URLs, and misleading subject lines.
- Image Hosting Management: Ensure reliable image hosting and avoid broken image links; consider branded URLs for AWS.
- Practice List Hygiene: Regularly clean your email list to remove outdated, inactive, or invalid addresses.
- Monitor Gmail Changes: Stay informed about potential changes in Gmail's interface and filtering practices.
- Review Welcome Email Strategies: Examine practices for sending welcome emails and monitor their spam reporting rates.
- IP Address Consistency: Check that your emails are sent from consistent and authorized IP addresses.
- Check user settings: Advise users on custom email safety and privacy settings.
What email marketers say
10 marketer opinions
Gmail flags emails with the 'Images are hidden, this message might be suspicious' banner for a variety of reasons related to sender reputation, authentication, and content. Improperly configured SPF, DKIM, and DMARC records can cause deliverability issues. A poor sender reputation, influenced by bounce rates, spam complaints, and blacklist inclusion, is a significant factor. Suspicious URLs, inconsistent sending IP addresses, and spam-like content also contribute. Furthermore, broken image links, the use of tracking pixels in cold outreach emails, and poor list hygiene (sending to outdated or invalid addresses) can trigger the warning.
Key opinions
- Authentication: Improperly configured SPF, DKIM, and DMARC records negatively impact email deliverability.
- Sender Reputation: A poor sender reputation, resulting from spam complaints, high bounce rates, and blacklisting, triggers the warning.
- Content Issues: Suspicious URLs, spam-like keywords, and misleading subject lines contribute to emails being flagged.
- Image & Tracking: Broken image links and the use of tracking pixels, especially in cold outreach, can cause issues.
- List Hygiene: Sending to outdated or invalid email addresses negatively impacts sender reputation.
Key considerations
- Email Authentication Setup: Ensure SPF, DKIM, and DMARC records are correctly configured to authenticate your emails.
- Sender Reputation Monitoring: Regularly monitor your sender reputation and take steps to address any issues, such as high bounce rates or spam complaints.
- Content Optimization: Avoid using spam-like keywords, suspicious URLs, and misleading subject lines in your email content.
- Image Hosting: Ensure image hosting is reliable and avoid broken image links.
- List Hygiene Practices: Regularly clean your email list to remove outdated, inactive, or invalid email addresses.
- IP Address Consistency: Ensure your emails are sent from consistent and authorized IP addresses.
Marketer view
Email marketer from HubSpot shares that sending emails to outdated, inactive, or invalid email addresses can result in high bounce rates and negatively affect sender reputation, causing Gmail to flag emails as suspicious.
26 Oct 2024 - HubSpot
Marketer view
Email marketer from Sender Score says that if you have a poor sender score, which is an indicator of your IP's reputation, you will be more likely to be flagged as suspicious. Regularly monitor your sender score for signs of issues.
29 Dec 2022 - Sender Score
What the experts say
7 expert opinions
Gmail's 'Images are hidden, this message might be suspicious' banner may be triggered by several factors, including Gmail testing new user interface elements, filtering algorithm changes, and issues with image URLs or CDNs. Problems with email authentication, short URLs, and domain reputation can also be contributing factors. Welcome emails are potentially handled differently due to spam reporting patterns. AWS image hosting issues are sometimes resolved by using branded URLs.
Key opinions
- Gmail Experiments: Gmail may be experimenting with its UI or filtering algorithms, leading to the banner.
- Image Issues: Image URLs and CDNs with poor reputations or hosting problems (e.g., AWS without branded URLs) can trigger the banner.
- Authentication Problems: Missing or broken email authentication contributes to the issue.
- Welcome Email Treatment: Welcome emails may be subject to stricter filtering due to spam reporting patterns.
- URL Reputation: Short URLs or URLs with poor reputations may cause the banner to appear.
Key considerations
- Monitor for Changes: Stay informed about potential changes in Gmail's interface and filtering practices.
- Check Image URLs: Ensure image URLs and CDNs have a good reputation and are functioning correctly.
- Implement Authentication: Implement proper email authentication (SPF, DKIM, DMARC).
- Review Welcome Email Practices: Review practices for sending welcome emails and monitor their spam reporting rates.
- Avoid Short URLs: Avoid using short URLs in emails if possible, and ensure linked domains have a good reputation.
- Branded URLs for AWS: If using AWS for image hosting, use branded URLs instead of the default s3.* moniker.
Expert view
Expert from Word to the Wise shares that several issues cause the warning, including missing or broken authentication, using short URLs, or the URL having a bad reputation.
12 Jul 2024 - Word to the Wise
Expert view
Expert from Email Geeks believes Google might be changing their filtering mechanisms and how they communicate these changes to users.
14 Dec 2023 - Email Geeks
What the documentation says
5 technical articles
Gmail flags emails with the 'Images are hidden, this message might be suspicious' banner when senders fail to adhere to Gmail's guidelines, which include proper email authentication, avoiding spammy content, and maintaining a good sender reputation. Incorrectly configured SPF records, DMARC policy failures (where SPF and DKIM don't align), and missing or invalid DKIM signatures prevent Gmail from verifying email authenticity, leading to suspicion. Moreover, personal safety or privacy settings can trigger automatic flagging.
Key findings
- Gmail Guidelines: Non-compliance with Gmail's sender guidelines triggers warnings.
- SPF Configuration: Incorrectly configured SPF records cause deliverability issues.
- DMARC Policy: DMARC policy failures, such as SPF and DKIM misalignment, lead to flagged emails.
- DKIM Signatures: Missing or invalid DKIM signatures prevent authentication.
- User Settings: Personal safety or privacy settings can trigger automatic flagging of emails.
Key considerations
- Adhere to Gmail Guidelines: Follow Gmail's best practices for senders.
- Correct SPF Configuration: Ensure SPF records are correctly configured and tested.
- Implement DMARC: Implement DMARC policy and ensure SPF and DKIM alignment.
- Valid DKIM Signatures: Use valid DKIM signatures to authenticate your emails.
- User Customization: Consider user privacy settings may trigger the banner warning
Technical article
Documentation from RFC explains that an incorrectly configured SPF record, such as one that is too broad or contains errors, can cause Gmail to treat emails with suspicion, as it can't properly verify the sender's legitimacy.
29 Sep 2023 - RFC
Technical article
Documentation from DMARC.org clarifies that when DMARC policy fails (e.g., SPF and DKIM don't align), Gmail may flag emails as suspicious to protect users from potential phishing or spoofing attacks.
9 Apr 2022 - DMARC.org
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