Summary
Emails bouncing with REASON 552 5.7.0 in Gmail are generally blocked due to content that triggers Gmail's security filters or violates their policies. The issue could stem from suspicious links (especially shortened ones or those redirecting to potentially malicious sites), email addresses embedded in tracking URLs, spam trigger words or phrases, file types, or a poor sender reputation. Resolutions involve carefully reviewing email content, inspecting link destinations, implementing strong email authentication (SPF, DKIM, DMARC), warming up IP addresses, testing content against spam filters, managing bounce and complaint rates, and ensuring adherence to Google's policies. If routing emails through Exchange Online, Microsoft's outbound spam filters may also contribute to the bounce.
Key findings
- Content Triggers: Gmail's spam filters are highly sensitive to specific words, phrases, and content types, potentially leading to bounces.
- Link Issues: Suspicious or shortened links, especially those with redirects, and email addresses embedded in tracking URLs can be flagged.
- Sender Reputation Impacts: A poor sender reputation, indicated by factors such as low engagement, high complaint rates, and lack of authentication, greatly increases the likelihood of emails being blocked.
- Authentication Crucial: Proper email authentication (SPF, DKIM, DMARC) is essential for verifying sender identity and improving deliverability; its absence is a common cause for emails getting marked as spam.
- External Filters Play a Role: Microsoft's outbound spam filters may flag the email when routing emails through Exchange Online.
Key considerations
- Content Review is Paramount: Thoroughly review email content, including subject lines, message bodies, links, and attachments, to identify and eliminate potentially problematic elements.
- URL Inspection is Key: Use URL checkers and expanders to carefully inspect link destinations, ensuring they are safe and legitimate.
- Spam Filter Testing: Utilize email testing tools to pre-emptively assess email content against spam filters and identify triggers before sending.
- Authentication Implementation is a Must: Implement and regularly verify that SPF, DKIM, and DMARC are correctly configured for all sending domains.
- Sender Reputation Management Requires Vigilance: Proactively manage sender reputation by monitoring bounce and complaint rates, warming up new IP addresses, and engaging with subscribers to build trust.
- Policy Adherence is Non-Negotiable: Familiarize yourself with and adhere to the email sending policies of all relevant providers (e.g., Google, Microsoft).
- A/B Testing to Optimize Deliverability: Use A/B testing of different email elements to identify and implement practices that optimize email deliverability.
What email marketers say
14 marketer opinions
Emails bouncing with the REASON 552 5.7.0 error in Gmail are typically blocked due to content being flagged as a potential security risk or triggering spam filters. Common causes include suspicious links (especially those shortened or with redirects), email addresses embedded in tracking URLs, specific words/phrases, certain file types, and a poor sender reputation. Solutions involve reviewing email content for problematic elements, implementing strong email authentication (SPF, DKIM, DMARC), warming up IP addresses, testing email content against spam filters, and maintaining consistent sending volumes.
Key opinions
- Content triggers: Gmail’s spam filters are sensitive to specific words, phrases, and content types, leading to bounces.
- Links: Suspicious or shortened links, especially those with redirects, and email addresses embedded in tracking URLs are often flagged.
- Sender Reputation: A poor sender reputation, indicated by factors like low engagement, high complaint rates, and lack of authentication, contributes to blocking.
- Authentication: Lack of proper email authentication (SPF, DKIM, DMARC) can cause emails to be marked as spam.
Key considerations
- Content Review: Carefully review email content, including subject lines, message bodies, links, and attachments, for anything that could be flagged as suspicious or malicious.
- URL Inspection: Use URL checkers and expanders to inspect the destinations of links in emails.
- Email Testing: Test email content against spam filters before sending to identify and remove problematic elements.
- Authentication Implementation: Implement and verify proper email authentication protocols (SPF, DKIM, DMARC) to confirm sender identity and improve deliverability.
- Sender Reputation Management: Monitor and maintain a positive sender reputation by managing bounce and complaint rates, warming up IPs, and engaging with subscribers.
- A/B Testing: Use A/B testing to optimize different email elements and identify what works best with Gmail's filters.
Marketer view
Marketer from Email Geeks shares that bounces were caused by email addresses in pixel/tracking links, and using subscriber IDs instead resolved the issue.
15 Dec 2023 - Email Geeks
Marketer view
Email marketer from Campaign Monitor advises implementing strong email authentication protocols (SPF, DKIM, DMARC) to verify the sender's identity and improve email deliverability. They provide guides on how to set up these protocols correctly.
27 Feb 2022 - Campaign Monitor
What the experts say
4 expert opinions
Emails bouncing with REASON 552 5.7.0 in Gmail typically indicate content or link issues that trigger spam filters or potential security concerns. The problem can stem from malicious links, compromised hosting sites, or issues with email authentication. Identifying commonalities across bounced emails, scrutinizing content for spam triggers, and verifying email authentication are crucial steps for resolution.
Key opinions
- Content Scrutiny: Email content is heavily scrutinized by Gmail's spam filters for suspicious elements.
- Link Security: Links, particularly those leading to compromised domains or phishing sites, are significant contributors to bounces.
- Authentication Importance: Email authentication issues (SPF, DKIM, DMARC) can cause emails to be flagged as spam.
- Common Link Analysis: Identifying commonalities in links across bounced emails can pinpoint the source of the problem.
Key considerations
- Examine Content and Links: Thoroughly examine email content and links for anything that might trigger spam filters or lead to malicious websites.
- Check Email Headers: Inspect email headers for more detailed information about the cause of the bounce.
- Verify Authentication: Ensure proper email authentication (SPF, DKIM, DMARC) is in place to verify the sender's identity.
- Identify Vulnerabilities: Identify and address any vulnerabilities with hosting sites or third-party providers.
Expert view
Expert from Email Geeks suggests examining the content and links of the messages causing bounces, especially for domains hosting phishing or malware sites.
4 May 2022 - Email Geeks
Expert view
Expert from Word to the Wise, Laura Belgray, explains the error often arises from spam filters, which scrutinize email content for specific triggers. She recommends avoiding excessive use of spam trigger words, being mindful of link destinations, and ensuring your content aligns with audience expectations.
19 Aug 2022 - Word to the Wise
What the documentation says
4 technical articles
Emails bouncing with the REASON 552 5.7.0 error in Gmail are blocked due to content presenting a potential security issue, as determined by Gmail's spam filters or policy restrictions. While the specific error isn't always detailed in standard documentation, it generally signifies a problem with email content, sender policies, or authentication, leading to the email being flagged as potentially malicious. This can be related to content filtering or broader policy enforcements. If routing emails through Exchange Online, Microsoft's filters may also flag the content.
Key findings
- Content Security: The primary cause is identified as a potential security issue within the email's content.
- Policy Restrictions: The bounce can stem from content filtering or policy restrictions imposed by the receiving mail server.
- Authentication and Policy: Ensuring adherence to email best practices, content guidelines, and robust authentication is crucial for deliverability.
- External Filtering: If using Exchange Online, Microsoft's spam filters may contribute to the bounce.
Key considerations
- Content Review: Review email content meticulously for potential security risks, spam triggers, and policy violations.
- Policy Compliance: Ensure compliance with the sending policies of email providers like Google and Microsoft.
- Authentication Setup: Implement and verify the correct configuration of SPF, DKIM, and DMARC for domain authentication.
- Domain Configuration: Verify that your domains are correctly configured within your email sending platform.
Technical article
Documentation from Google Support explains that the error message '552 5.7.0 This message was blocked because its content presents a potential security issue' indicates that Gmail blocked the message due to suspected malicious content. They advise reviewing Google's policies to ensure compliance.
7 Mar 2022 - Google Support
Technical article
Documentation from Postmark explains while Postmark does not have information specific to the Gmail 552 5.7.0 error code, Postmark says this error code often signals a problem with email content as perceived by the recipient server's security policies. Ensuring emails adhere to best practices for content and authentication can improve deliverability.
5 Apr 2025 - Postmark
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