Summary
Gmail employs sophisticated machine learning algorithms, informed by signals like sender reputation, content characteristics, and email authentication, to identify and block phishing attempts. Core issues that trigger these filters include poor sender reputation (due to low engagement, high bounce rates, or blocklist inclusions), suspicious content within the email (malicious links, keywords, or attachments), sending from shared IPs with bad reputations, inconsistent sending patterns, and a lack of proper email authentication using SPF, DKIM, and DMARC records. Additionally, Google maintains its own list of bad URLs, and compromised websites or linked content can lead to emails being flagged. Sudden spikes in email volume also contribute to triggering spam filters.
Key findings
- ML-Based Detection: Gmail employs machine learning models to detect phishing attempts, analyzing numerous factors.
- Sender Reputation: Poor sender reputation stemming from low engagement, high bounce rates, or blocklisting significantly increases the risk.
- Suspicious Content: Malicious links, keywords, and attachments trigger phishing filters.
- Email Authentication: Lack of SPF, DKIM, and DMARC records makes emails appear less trustworthy and more likely to be flagged.
- Google's URL List: Google maintains a private list of URLs deemed malicious, impacting email deliverability.
- Website Compromise: A compromised website or linked content can lead to emails being flagged as phishing.
- Inconsistent Volume: Sudden spikes in email sending volume trigger spam filters.
- Shared IPs: Shared IP addresses impact the sender reputation
- Personalisation: Not personalising emails, especially the from and reply-to address can reduce deliverability
Key considerations
- Improve Sender Reputation: Focus on improving sender reputation by authenticating emails, cleaning email lists, and sending engaging content.
- Scrub Suspicious Content: Avoid using suspicious links, keywords, or attachments in your emails.
- Authenticate Emails: Implement and verify SPF, DKIM, and DMARC records to properly authenticate your emails.
- Monitor Blocklists: Regularly monitor your IP address and domain on blocklists.
- Investigate Compromises: If flagged, investigate and resolve any security issues that may have compromised your website or sending infrastructure.
- Gradual Volume Increase: Increase email volume gradually and warm up your IP address to avoid triggering spam filters.
- Remove bad links: Remove any blacklisted or malicious links
- Personalise emails: Personalise emails and make sure that the from and reply-to address are valid
What email marketers say
7 marketer opinions
Gmail flags emails as phishing for a variety of reasons related to sender reputation, content, and authentication. Poor sender reputation, often stemming from low engagement, high bounce rates, or blocklist inclusion, is a primary cause. Suspicious content, such as malicious links, keywords, or attachments, also triggers phishing filters. Sending from a shared IP with a bad reputation or exhibiting inconsistent sending patterns exacerbates the issue. Finally, failing to properly authenticate emails with SPF, DKIM, and DMARC records leaves them vulnerable to being flagged as phishing attempts. Personalization can help to improve deliverability.
Key opinions
- Sender Reputation: Poor sender reputation due to low engagement, high bounce rates, or blocklisting is a major factor.
- Suspicious Content: The presence of malicious links, keywords, or attachments can trigger phishing filters.
- Shared IPs: Sending from a shared IP with a poor reputation increases the likelihood of being flagged.
- Inconsistent Sending: Inconsistent sending patterns, such as sudden spikes in volume, can trigger spam filters.
- Authentication: Missing or incorrect SPF, DKIM, and DMARC records make emails appear less trustworthy.
- Personalisation: Personalising emails by checking the from and reply-to address can improve deliverability.
Key considerations
- Improve Sender Reputation: Authenticate emails, clean email lists, and send engaging content to improve your sender reputation.
- Avoid Suspicious Content: Ensure that links point to legitimate websites and avoid using suspicious keywords or attachments.
- Dedicated IP: Consider using a dedicated IP address to maintain control over your sender reputation.
- Consistent Sending: Establish consistent sending patterns and gradually increase sending volume.
- Email Authentication: Implement and verify SPF, DKIM, and DMARC records to authenticate your emails.
- Check blocked links: Ensure the links are not blacklisted.
- Personalise emails: Personalise emails, especially the from and reply-to address can improve deliverability
Marketer view
Email marketer from Reddit explains that inconsistent sending practices can lead to Gmail flagging emails as phishing. Suddenly sending a large volume of emails or changing sending patterns can trigger Gmail's spam filters.
28 Dec 2024 - Reddit
Marketer view
Email marketer from Mailgun shares that a common reason for Gmail flagging emails as phishing is poor sender reputation. This can be due to low engagement rates, high bounce rates, or being listed on blocklists. They recommend improving sender reputation by authenticating emails, cleaning email lists, and sending engaging content.
3 Nov 2022 - Mailgun
What the experts say
6 expert opinions
Gmail marks emails as phishing due to a combination of factors, including Google's private list of bad URLs, indications of phishing activity detected by multiple ISPs, potential compromise of a brand's website hosting a phishing target page, lack of proper email authentication (SPF, DKIM, DMARC), and sudden spikes in email volume. The core issue often involves compromised links or a lack of sender verification, leading Gmail to flag the emails as potentially harmful.
Key opinions
- Google's Bad URL List: Google maintains a private list of URLs that it considers malicious.
- Phishing Indicators: Multiple ISPs reporting phishing activity in your emails is a strong indicator of an actual problem.
- Website Compromise: A brand's website might be compromised, hosting a phishing target page that's triggering blocks.
- Authentication Issues: Lack of proper SPF, DKIM, and DMARC records can lead to emails being flagged as phishing attempts.
- Volume Spikes: Sudden increases in email volume can trigger spam filters.
Key considerations
- Remove Phishing Site: Identify and remove any phishing sites hosted on your domain.
- Implement Authentication: Implement and verify SPF, DKIM, and DMARC records to authenticate your emails.
- Gradual Volume Increase: Gradually increase email volume and warm up your IP address to avoid triggering spam filters.
- Check linked pages: Check linked pages for malicious content.
Expert view
Expert from Email Geeks explains that Google runs its own private list of bad URLs.
20 Nov 2022 - Email Geeks
Expert view
Expert from Spam Resource suggests that emails are being flagged as phishing due to a lack of proper authentication (SPF, DKIM, DMARC). Implementing these correctly is crucial for proving the legitimacy of your emails to Gmail.
2 Jan 2022 - Spam Resource
What the documentation says
4 technical articles
Gmail employs sophisticated machine learning models to detect phishing attempts by analyzing sender information, message content, and links. A key factor is email authentication (SPF, DKIM, DMARC); lack of it increases the likelihood of emails being flagged. Additionally, being listed on blocklists like Spamhaus due to a compromised IP or domain significantly contributes to Gmail marking emails as phishing.
Key findings
- ML Detection: Gmail uses machine learning to identify suspicious characteristics in messages and evolve to detect new patterns.
- BEC Detection: Improved models specifically target business email compromise (BEC) attacks.
- Authentication Importance: Email authentication (SPF, DKIM, DMARC) is crucial for sender verification and preventing spoofing.
- Blocklist Impact: Listing on blocklists like Spamhaus leads to emails being flagged as spam or phishing.
Key considerations
- Implement Authentication: Ensure proper setup of SPF, DKIM, and DMARC records to authenticate your emails.
- Monitor Blocklists: Regularly monitor your IP address and domain on blocklists like Spamhaus.
- Address Compromises: If listed on a blocklist, investigate and resolve any security issues that may have led to the listing.
Technical article
Documentation from Google Security Blog shares that Google has improved its machine learning models to better detect business email compromise (BEC) attacks, a type of phishing. These models analyze signals such as sender authentication, email routing, and content characteristics to identify and block malicious messages.
3 Dec 2021 - Google Security Blog
Technical article
Documentation from Google Workspace Admin Help explains that Gmail's phishing detection identifies suspicious characteristics in messages, using machine learning models that evolve to identify new patterns. It analyzes various factors like sender information, message content, and links to determine if a message is phishing.
17 Apr 2024 - Google Workspace Admin Help
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