Why is Gmail flagging messages as suspicious due to low sender reputation?

Key findings

• Sender reputation: Gmail heavily relies on sender reputation, which is influenced by a multitude of factors, including spam complaints, engagement rates, and domain history.
• Authentication: Proper implementation of email authentication protocols like SPF, DKIM, and DMARC is essential for Gmail to trust your messages. Misconfigurations can severely impact deliverability, as Gmail looks for a complete authentication picture.
• Content quality: Spammy language, suspicious links, and deceptive practices can trigger Gmail's phishing filters, regardless of your authentication setup.
• Volume and consistency: Sudden spikes in sending volume or inconsistent sending patterns from an IP address with a poor history can raise red flags.
• IP and domain reputation: Both the IP address and the sending domain contribute to your overall reputation. A low reputation on either can lead to messages being blocked or sent to the spam folder. For further guidance on this, read our article a practical guide to understanding your email domain reputation.

Key considerations

• Monitor deliverability: Regularly check your email deliverability rates and monitor for bounces, especially those indicating low reputation.
• Review sending practices: Assess your list acquisition methods, email content, and sending frequency to identify potential issues contributing to low reputation. You can read more in Mailgun's guide on preventing Gmail from blocking emails.
• Engage subscribers: Encourage positive engagement (opens, clicks) and provide easy unsubscribe options to reduce spam complaints.
• Segment lists: Send targeted content to engaged segments of your audience to improve relevance and engagement.
• Authentication hygiene: Regularly test and ensure your SPF, DKIM, and DMARC records are correctly configured and aligned.

Key opinions

• Sudden onset: Some marketers observed a sudden increase in these Gmail rejections around the beginning of the year, leading them to question if Gmail had implemented new rules.
• Client behavior vs. rule changes: There's a debate on whether the problem is due to clients' poor list hygiene and sending practices, or if Gmail has indeed shifted its filtering policies more aggressively.
• Impact on clients: The issue caused significant distress among clients experiencing these bounce messages, highlighting the severe impact on their email campaigns.
• Broad reputation factors: Some suggested that the low reputation could be based on broader, possibly external, factors beyond direct sending metrics.

Key considerations

• Identify the cause: Marketers should thoroughly investigate whether their low reputation is a result of their own sending patterns (e.g., poor list quality) or changes in ISP algorithms.
• Adapt sending behavior: Regardless of whether rules are new or old, adapting sending practices to align with Gmail's expectations is critical. This includes improving domain reputation and IP health.
• Monitor engagement closely: Low engagement rates and high spam complaint rates are significant indicators of poor sender reputation, requiring immediate attention. EmailLabs discusses this in more detail in their article on sender reputation.
• Review list hygiene: A very bad list is a strong contender for why these issues appear. Cleaning lists and removing inactive subscribers can help.

Key opinions

• Dynamic rule changes: Experts agree that Gmail is constantly modifying its filtering rules, making it difficult to pinpoint a single, scheduled change causing reputation issues.
• Behavioral impact: The core issue often lies with sender behavior, such as sending to unengaged lists or exhibiting patterns associated with spam.
• Holistic reputation: Reputation isn't just about IP; it encompasses domain, content, and user engagement signals, all of which contribute to how Gmail views a sender.
• No set schedule for changes: There isn't a predictable yearly schedule for Gmail to switch up its reputation rules; changes happen continuously based on observed traffic and threat landscapes.

Key considerations

• Focus on core deliverability principles: Regardless of minor algorithm tweaks, adherence to fundamental best practices, like list hygiene and segmenting, is always paramount.
• Monitor specific error messages: Pay close attention to bounce codes like 550-5.7.1, as they provide direct feedback from Gmail about reputation issues.
• Address engagement and spam complaints: These are direct signals to Gmail about recipient sentiment. High rates indicate a serious reputation problem. Our guide on suspicious message alerts provides further insight.
• Utilize Postmaster Tools: Google Postmaster Tools is an invaluable resource for gaining insight into your domain and IP reputation as seen by Gmail.

Key findings

• Sender reputation metrics: Gmail's systems evaluate sender reputation based on multiple factors including spam rate, IP reputation, domain reputation, and user feedback.
• Authentication compliance: Full authentication (SPF, DKIM, DMARC) is critical. Misaligned or missing records can cause emails to be treated as suspicious, even if content is legitimate.
• Engagement signals: Low engagement (low open rates, high unsubscribe rates) can indicate poor sender quality and lead to reputation penalties, even if spam complaints are low.
• Content and links: Suspicious content or deceptive links are heavily scrutinized by phishing filters and can immediately trigger warnings or blocks.
• Blacklists and blocklists: Being listed on public or private blacklists (blocklists) significantly impacts IP and domain reputation, leading to deliverability issues.

Key considerations

• Utilize Postmaster Tools: Documentation strongly advises using Google Postmaster Tools to gain direct insights into your domain and IP reputation, spam rates, and delivery errors from Gmail's perspective. Our article on the Ultimate Guide to Google Postmaster Tools elaborates on this.
• Regularly audit authentication: Consistently test your SPF, DKIM, and DMARC setups to ensure they are correctly configured and aligned, as improper setup is a common cause of deliverability issues.
• Focus on list quality: Documentation often emphasizes the importance of permission-based lists and regular list cleaning to avoid spam traps and reduce complaints.
• Monitor blocklists: Although Gmail uses internal blocklists, being on external public blocklists can also impact your general sender reputation, making it important to monitor them.
• Follow email guidelines: Adhere to general email marketing best practices and Gmail's specific sender guidelines to ensure messages are seen as legitimate.