Summary
Even with correctly configured SPF and DKIM records, emails can still be blocked by Gmail for various reasons. While these authentication standards verify the sender, Gmail's sophisticated filtering system goes beyond basic checks, evaluating factors like DMARC alignment, the sender's overall reputation, email content, and user engagement. Transient network issues or improper technical setups like reverse DNS can also lead to deliverability problems.
Key findings
- DMARC Alignment Failures: While SPF and DKIM authenticate individual email aspects, DMARC requires the 'From' header domain to align with the domain authenticated by SPF or DKIM. If this alignment fails, DMARC policies, such as 'p=reject' or 'p=quarantine', will instruct Gmail to block the email, even if SPF and DKIM technically pass.
- Poor Sender Reputation: Gmail heavily weighs sender reputation, considering factors like IP address history, domain standing, spam complaint rates, bounce rates, and hits on spam traps. A low reputation, regardless of authentication status, can cause emails to be blocked or routed to spam.
- User Engagement Signals: Gmail's filtering is highly user-centric. Low engagement, such as recipients consistently marking emails as spam, deleting them without opening, or moving them to trash, negatively impacts sender reputation and can lead to blocks.
- Content-Related Issues: Even with perfect authentication, email content itself can trigger spam filters. This includes the use of spammy keywords, suspicious links, excessive images, or malicious attachments, which can cause emails to be flagged.
- Shared IP Address Reputation: For senders using shared IP addresses through an Email Service Provider, the sending habits and reputation of other users on that same IP can affect deliverability. A poor reputation from co-located senders can lead to Gmail blocking your emails.
- Transient DNS or Propagation Delays: Authentication failures can sometimes be temporary, resulting from transient DNS resolution issues or delays in DNS propagation for newly updated SPF or DKIM records.
- Reverse DNS (rDNS) Misconfiguration: Gmail performs rDNS lookups to verify the sending IP address. If the rDNS record is missing, misconfigured, or doesn't match the mail server's hostname, it can raise red flags and lead to blocks.
- Email Forwarding Interference: When an email is forwarded, especially if the forwarding server modifies headers, it can break the original SPF and DKIM signatures. Gmail may then block the forwarded message due to perceived authentication failure.
Key considerations
- Implement and Monitor DMARC: Ensure DMARC is properly configured with an appropriate policy, and actively monitor DMARC reports to identify alignment issues and gain insights into authentication failures.
- Prioritize Sender Reputation: Focus on building and maintaining a strong sender reputation by avoiding spam complaints, minimizing bounces through regular list cleaning, and never sending to spam traps.
- Cultivate Positive User Engagement: Encourage recipients to open, click, and reply to your emails. Design content that is valuable and relevant to minimize spam reports and maximize positive engagement signals.
- Optimize Email Content: Avoid elements commonly associated with spam, such as overly promotional language, suspicious links, or excessive imagery. Ensure your content is clean, clear, and trustworthy.
- Utilize Gmail Postmaster Tools: Regularly monitor your domain and IP reputation, spam rate, and authentication status through Google Postmaster Tools. This resource provides crucial insights into how Gmail perceives your sending practices.
- Maintain Excellent List Hygiene: Continuously clean your email lists to remove invalid, inactive, or unsubscribed addresses. Sending to a clean, engaged list is fundamental for positive deliverability outcomes.
- Understand Shared IP Risks: If using a shared IP, be aware that the actions of other senders can impact your deliverability. Consider a dedicated IP if volume and reputation justify it.
- Verify rDNS Configuration: Ensure that the reverse DNS record for your sending IP address is correctly configured and matches your mail server's hostname.
- Account for DNS Propagation: Allow sufficient time for DNS changes to propagate globally after updating SPF, DKIM, or DMARC records before sending large volumes of mail.
What email marketers say
9 marketer opinions
While Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) are essential for email authentication, their correct configuration doesn't guarantee deliverability to Gmail's inbox. Gmail employs a comprehensive filtering system that assesses numerous other factors. These include the enforcement of DMARC policies, the overall sender reputation of both the domain and sending IP, potential issues with shared IP addresses, and the accuracy of reverse DNS records. Additionally, transient network problems or even the act of email forwarding can inadvertently cause authentication failures, leading to blocks.
Key opinions
- DMARC Policy Enforcement: Even if SPF and DKIM pass individually, a DMARC record set to 'reject' or 'quarantine' will instruct Gmail to block emails if DMARC alignment fails, meaning the 'From' domain doesn't align with the authenticated domain.
- Dominant Sender Reputation: Beyond technical authentication, Gmail prioritizes the sender's reputation, which is influenced by factors like high spam complaint rates, excessive bounces, and interactions with spam traps. A poor reputation will lead to blocks.
- Impact of Shared IP Addresses: When sending through shared IP addresses via an Email Service Provider, the sending practices of other users on that IP can negatively affect your deliverability, regardless of your domain's perfect authentication.
- Reverse DNS (rDNS) Verification: Gmail often performs rDNS lookups. If the rDNS record for the sending IP is missing, incorrect, or doesn't match the server's hostname, it raises a red flag and can result in emails being blocked.
- List Quality and Sending Practices: Poor list hygiene, such as sending to invalid or old addresses, inconsistent sending frequency, or sudden, uncharacteristic volume spikes, signals poor sender behavior to Gmail, damaging reputation and causing blocks.
- Transient DNS or IP Problems: Authentication failures can sometimes be temporary, stemming from fleeting DNS resolution issues or temporary problems with the sending IP range, requiring re-attempts or checks with the ESP.
- Email Forwarding Disruption: The act of forwarding an email can modify headers, inadvertently breaking the original SPF and DKIM signatures. When Gmail receives such a forwarded message, it may block it due to the perceived authentication failure.
Key considerations
- Implement and Monitor DMARC Carefully: Ensure your DMARC record is correctly set up with an appropriate policy, and regularly review DMARC reports to identify and address any alignment issues.
- Proactively Manage Sender Reputation: Prioritize minimizing spam complaints, regularly cleaning your email lists to reduce bounces, and avoiding spam traps to maintain a strong IP and domain reputation.
- Understand Shared IP Implications: If using a shared IP, be aware that your deliverability can be influenced by others' sending habits, necessitating a choice of ESPs with strong shared IP management.
- Verify Reverse DNS Configuration: Confirm that the rDNS record for your sending IP address is properly configured and aligns with your mail server's hostname to avoid technical red flags.
- Maintain Rigorous List Hygiene: Continuously clean your email lists by removing invalid, unsubscribed, and inactive addresses to improve engagement metrics and signal good sending practices to Gmail.
- Assess for Temporary Issues: When an authentication problem occurs, first re-send the email to determine if the issue was transient, and if persistent, contact your Email Service Provider for insight into IP range health.
- Be Aware of Forwarding's Authentication Impact: Recognize that emails forwarded by recipients may encounter authentication failures, which is typically outside of your direct control but part of the deliverability landscape.
Marketer view
Marketer from Email Geeks explains that the authentication issue might be temporary and advises checking with the sender's ESP (Infobip) for any recent IP range issues.
8 May 2025 - Email Geeks
Marketer view
Marketer from Email Geeks responds that while DNS records (TXT for DKIM and SPF) appear to be correctly configured and returning results, the authentication failure likely indicates a transient DNS resolution issue. He suggests re-sending the email to see if the error persists, implying that if it doesn't, it was a temporary DNS problem.
26 Jun 2021 - Email Geeks
What the experts say
3 expert opinions
Gmail's blocking of emails, even when SPF and DKIM records are correctly set up, often stems from two primary issues: DMARC alignment failures and a poor sender reputation. While SPF and DKIM confirm a message's origin, DMARC adds a crucial layer by requiring the 'From' header domain to match the authenticated domain. If this alignment is missing, DMARC policies can instruct Gmail to reject or quarantine the email. Additionally, Gmail heavily weighs the sender's reputation, which encompasses factors like complaint rates and engagement, meaning a low reputation can lead to blocks regardless of successful authentication.
Key opinions
- DMARC Alignment is Crucial: Even when SPF and DKIM records pass, DMARC requires the domain in the 'From' header to align with the domain authenticated by SPF or DKIM. A failure in this alignment, especially under a strict DMARC policy (p=reject or p=quarantine), will lead to Gmail blocking the email.
- Sender Reputation Overrides Authentication: Beyond technical authentication, Gmail's filtering system significantly prioritizes sender reputation, which is influenced by metrics like complaint rates, bounce rates, and user engagement. A low sender reputation can cause emails to be filtered or blocked, regardless of valid SPF and DKIM.
Key considerations
- Ensure DMARC Alignment: Proactively configure and monitor DMARC records to ensure the 'From' header domain consistently aligns with your SPF or DKIM authenticated domains, especially with strict DMARC policies.
- Prioritize Sender Reputation Management: Consistently work to build and maintain a strong sender reputation by minimizing spam complaints, managing bounce rates, avoiding spam traps, and encouraging positive user engagement. These factors can override successful authentication.
Expert view
Expert from Spam Resource explains that even with correctly configured SPF and DKIM, emails can be blocked by Gmail if they fail DMARC alignment checks. DMARC requires the domain in the 'From' header to align with the domain used for SPF (organizational or exact) or DKIM (organizational or exact). If this alignment fails, even if SPF and DKIM pass, DMARC can cause the email to be rejected or quarantined, especially when the DMARC policy is set to 'reject' or 'quarantine'.
1 Mar 2025 - Spam Resource
Expert view
Expert from Word to the Wise explains that emails can be blocked by Gmail despite correct SPF and DKIM records due to DMARC failures. DMARC introduces an alignment requirement, meaning the 'From' domain must match the domain in the SPF or DKIM signature. If this alignment fails, even with valid SPF and DKIM, DMARC will fail, leading to rejection or spam folder placement, particularly if the sender's DMARC policy is set to 'reject' or 'quarantine'.
14 Jan 2025 - Word to the Wise
What the documentation says
6 technical articles
Beyond the foundational SPF and DKIM authentication, Gmail's sophisticated filtering system may still block emails due to several advanced factors. Crucially, a failure in DMARC alignment-where the 'From' header domain does not match the authenticated domain-can lead to rejections based on strict DMARC policies. Moreover, factors entirely separate from authentication, such as problematic email content, the presence of the sender's IP address on blacklists, or poor user engagement, significantly impact sender reputation and thus deliverability. Technical aspects like the absence of TLS encryption and insufficient DNS propagation time after record updates can also contribute to emails being blocked or flagged.
Key findings
- DMARC Alignment Failures Remain Key: Even with valid SPF and DKIM records, DMARC requires the 'From' header domain to align with the authenticated domain. A failure here, especially with 'p=reject' or 'p=quarantine' policies, will cause Gmail to block emails.
- Content and IP Blacklisting Issues: Email content featuring spammy keywords, suspicious links, excessive images, or malicious attachments can trigger spam filters. Additionally, if the sending IP address is on blacklists, emails will likely be blocked irrespective of authentication.
- User Engagement Directly Impacts Reputation: Gmail heavily factors in user behavior. Consistent negative signals like spam reports, deletions without opening, or moving to trash severely degrade sender reputation, leading to blocks even with technically correct authentication.
- TLS Encryption for Trust: While not a direct authentication mechanism, the absence of proper Transport Layer Security (TLS) encryption during email transmission can lower a sender's overall trust score with secure receiving servers like Gmail, contributing to increased filtering.
- Gmail Postmaster Tools Indicate Issues: A 'bad' or 'low' reputation status for your domain or IP in Google Postmaster Tools, regarding spam rate or authentication, is a strong indicator of why emails might be blocked, even if SPF, DKIM records are technically passing.
- DNS Propagation Delays: New or updated SPF and DKIM records require time to propagate across the internet. If emails are sent before full propagation, Gmail may query outdated DNS records, resulting in apparent authentication failures.
Key considerations
- Prioritize DMARC Alignment & Monitoring: Ensure DMARC is correctly configured with alignment, and actively review DMARC reports to detect and rectify any alignment issues or authentication failures.
- Optimize Email Content & Monitor IP Health: Carefully craft email content to avoid spam triggers. Regularly check if your sending IP addresses are listed on any major blacklists and address issues promptly.
- Foster Positive User Engagement: Actively work to improve recipient engagement by sending relevant, valuable content. Encourage opens, clicks, and replies to build a strong sender reputation with Gmail.
- Ensure TLS Encryption: Implement and verify that your email transmissions are secured with Transport Layer Security (TLS) to enhance trust and avoid potential filtering by secure mail servers.
- Leverage Google Postmaster Tools: Consistently use Google Postmaster Tools to monitor your domain and IP reputation, spam rates, and authentication status, using these insights to proactively address deliverability concerns.
- Account for DNS Propagation Time: After making any changes to SPF, DKIM, or DMARC DNS records, allow sufficient time for global propagation before resuming high-volume email sending.
Technical article
Documentation from Google Workspace Admin Help explains that while SPF and DKIM authenticate individual aspects of an email, DMARC requires 'alignment' between the 'From' header domain and the domain authenticated by SPF or DKIM. If this alignment fails, even with valid SPF and DKIM records, DMARC policies (p=reject or p=quarantine) will instruct receiving servers like Gmail to block or flag the email.
28 Nov 2024 - Google Workspace Admin Help
Technical article
Documentation from SendGrid Documentation highlights that even with correct SPF/DKIM/DMARC, email content can trigger spam filters. This includes using spammy keywords, suspicious links, excessive images, or malicious attachments. Additionally, the sending IP address might be on various blacklists, leading to blocks regardless of authentication.
13 May 2024 - SendGrid Documentation
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