Why are my emails going to spam in Gmail even though everything seems technically correct?

Key findings

• Content similarity: Gmail's systems can flag emails that are similar to messages identified as spam in the past, regardless of technical correctness.
• One-click unsubscribe (RFC8058): Google now requires support for RFC 8058 one-click list-unsubscribe for bulk senders as of June 1, 2024. Non-compliance can lead to emails not being delivered.
• Shared domains for assets: Using shared domains to host images or other assets (e.g., from a CDN or ESP's default domain) can negatively impact deliverability, especially for new sending domains, as it associates your content with the reputation of that shared domain.
• New domain reputation: A new sending domain without established reputation can face immediate deliverability challenges, even if warm-up is attempted with new subscribers. This is a common factor for emails going to spam for new Gmail recipients.
• Sender reputation nuances: A good sender score or general setup might not be enough if other factors like engagement or historical content issues are at play.

Key considerations

• Content review: Carefully review email content for anything that might trigger spam filters, such as certain keywords, excessive images, or poor formatting, which can cause Gmail emails to land in spam.
• RFC8058 compliance: Prioritize implementing the RFC8058 one-click unsubscribe header. This is a critical factor for Gmail deliverability, especially for promotional or bulk emails, as outlined by Google's new requirements.
• Domain alignment: Ensure all domains used for tracking, links, and image hosting are aligned with your sending domain. Inconsistent domain usage can appear suspicious to spam filters, particularly when using multiple email service providers (ESPs) or customer data platforms (CDPs).
• Sender authentication: Verify that your SPF, DKIM, and DMARC records are correctly configured and aligned. Even if they pass, misconfigurations can lead to deliverability issues, particularly with DMARC policies. For guidance, use a free DMARC record generator tool.
• Monitor engagement: Low engagement (opens, clicks) and high complaint rates (emails marked as spam) are significant negative signals for Gmail. Even with perfect technical setup, consistent negative engagement can lead to emails being filtered into spam.

Key opinions

• Content is king: Many marketers emphasize that if an email's content looks like spam or is uninteresting to recipients, it will be flagged, irrespective of technical setup. This is often the first area they review when troubleshooting. As one marketer puts it, poor subject lines to keywords that trigger spam filters can be culprits.
• Sender reputation complexity: Even with a good Google Postmaster Tools reputation, emails can still go to spam if other factors suggest unwanted mail. Marketers often note that reputation is multifaceted.
• New domain challenges: A new sending domain lacks historical reputation, making it more susceptible to spam filtering, even if warming up is attempted with engaged new subscribers.
• Authentication updates: Compliance with the latest authentication requirements, such as RFC 8058 one-click unsubscribe, is increasingly vital. What wasn't an issue before can now cause major deliverability problems.

Key considerations

• Subscriber engagement: Encourage positive engagement and promptly remove unengaged subscribers to improve inbox placement. High open rates and low spam complaint rates are key indicators of desired mail.
• List hygiene: Avoid sending to compromised addresses or lists acquired from dubious sources, as this can quickly damage your sender reputation and lead to emails going to spam even with a low spam rate.
• Domain alignment for assets: Ensure all hosted content (images, links) aligns with your primary sending domain. A weird mix of image hosting can appear suspicious to filters.
• Monitor blocklists: Regularly check if your IP or domain is on any email blocklists or blacklists, as this significantly impacts deliverability to Gmail and other providers.

Key opinions

• Content is paramount: The phrase 'similar to messages identified as spam' strongly indicates a content-related issue, suggesting Google's algorithms detect patterns in the email's content that resemble unwanted mail.
• RFC8058 is critical: Missing the RFC8058 one-click unsubscribe header is now a significant problem for deliverability to Gmail, especially since June 1, 2024. Prior success without it does not guarantee future deliverability.
• Mixed image hosting: A mix of image hosting domains (e.g., Cloudfront, Exponea, other CDNs) can appear suspicious to Gmail filters, as it is a tactic used by bad actors.
• New domain vulnerability: New domains without an established history of sending wanted email are more susceptible to filtering, making compliance with all measurable requirements even more crucial. Learn how to recover domain reputation.
• Evolving requirements: Inbox providers continually update their filtering criteria. What was acceptable last year may be an issue now, emphasizing the need for ongoing compliance and vigilance.

Key considerations

• Align all domains: Ensure all image hosting, click-tracking, and link domains are consistent and aligned with the primary sending domain to avoid suspicious patterns. This is vital for strong email authentication.
• Proactive compliance: Do not rely on past deliverability if new requirements are introduced. Proactively implement new standards like RFC8058, even if they haven't caused problems before.
• Monitor deliverability metrics: Pay close attention to Gmail's Postmaster Tools data, specifically the spam rate, reputation, and authentication metrics. This provides insights into how Gmail perceives your mail.
• Content optimization: Continuously test and refine email content to reduce similarities to known spam, focusing on clear, concise, and engaging messages relevant to your audience.
• Engaged audience: Maintaining a highly engaged subscriber list is one of the strongest signals of legitimate mail. Focus on consent-based acquisition and provide value to your recipients.

Key findings

• RFC 8058 mandate: As of June 1, 2024, Google explicitly requires email headers to support RFC 8058 one-click list-unsubscribe for bulk senders. Failure to comply directly impacts deliverability.
• Sender reputation weighting: Documentation often implies that a sender's historical reputation, including complaint rates and engagement, heavily influences filtering decisions, even when authentication passes. This aligns with Google Postmaster Tools guidance.
• Content analysis: Filtering systems, as described in various documentation, use advanced algorithms to analyze email content for spam-like characteristics, including similarity to previously identified spam messages.
• Domain alignment: Best practices for email authenticity and anti-spoofing suggest consistent domain usage across all parts of an email, including image hosting and links, to build trust with receiving servers.

Key considerations

• Prioritize RFC 8058: Senders must ensure their email service provider (ESP) or internal sending system fully supports and implements the RFC 8058 header to meet Gmail’s requirements for one-click unsubscribe.
• Holistic sender view: Understand that while SPF, DKIM, and DMARC are crucial, they are part of a broader set of signals Gmail uses. Focus on overall email program health, including engagement and content quality.
• Align all subdomains: Ensure all subdomains used for link tracking and image hosting are properly authenticated (e.g., via DKIM) and are associated with your primary sending domain to avoid suspicious indicators.
• Monitor evolving guidelines: Regularly consult official postmaster pages from major inbox providers (like Google and Yahoo) to stay informed about new or updated requirements.