Summary
When emails sent through Customer.io using SendGrid are not delivering as expected, it often indicates a combination of integration issues, deliverability settings, or underlying reputation problems. Initial reports from Customer.io may not always provide sufficient detail, necessitating a deeper dive into SendGrid's specific logs and metrics. Common culprits range from incorrect API key setup, to recipient-side filtering, or even rate limiting imposed by receiving mail servers.
Key findings
- Limited visibility: Customer.io's native reports, especially for bounces and failures, may not always provide granular enough detail to pinpoint specific delivery issues when using an external SMTP like SendGrid.
- SendGrid logs are crucial: The SendGrid activity feed and suppression lists offer more in-depth insights into why emails are not reaching inboxes, including specific bounce reasons and blocks.
- Integration and configuration: Incorrect setup or misconfiguration between Customer.io and SendGrid, particularly when using custom SMTP, can prevent delivery data from flowing correctly or impact sending.
- Rate limiting: Recipient mail servers (like Gmail) may temporarily reject emails if the sending volume from your IP or domain exceeds their set limits, leading to deferred bounces or blocks.
- Gmail specific issues: Many deliverability challenges, including low delivery rates or emails going to spam, are often observed with Gmail due to their strict filtering algorithms.
Key considerations
- Verify SendGrid integration: Ensure your SendGrid account is properly linked and configured within Customer.io, especially if using custom SMTP. An integration issue can prevent delivery data from syncing back correctly.
- Examine SendGrid activity: Regularly check your SendGrid activity feed and suppression lists for detailed reasons behind non-delivery, such as bounces, blocks, or invalid recipients.
- Address rate limits: If rate limiting is identified as a bounce reason, adjust your sending patterns or warm up your IPs to align with recipient server expectations. This is crucial for maintaining a good sender reputation, as discussed in our guide on recovering domain reputation.
- Monitor deliverability: Use tools or manual checks to monitor your inbox placement rates and identify if emails are landing in spam folders or not appearing at all, even when reported as delivered. For more on this, see why emails aren't appearing in the inbox.
What email marketers say
Email marketers often face frustrating deliverability issues when using platforms like Customer.io with external email service providers (ESPs) such as SendGrid. The initial problem reported was a low delivery rate of 20%, specifically to Gmail, despite SendGrid showing 50% requests. This highlights a common challenge: understanding where the breakdown occurs between the ESP's reported delivery and actual inbox placement, or even if the email left the ESP at all.
Key opinions
- Limited native reporting: Marketers frequently find that the deliverability reports within marketing automation platforms like Customer.io can be unclear or insufficient, especially when using a third-party sending service like SendGrid.
- Reliance on ESP logs: It's a common practice for marketers to dig into the detailed logs provided by their ESP (e.g., SendGrid's activity feed) to get a clearer picture of email statuses beyond what the marketing platform shows.
- Importance of bounce reasons: Understanding specific bounce codes and reasons is critical for diagnosing deliverability problems. Generic failed messages within Customer.io don't offer enough actionable data.
- Impact of rate limiting: Rate limiting by receiving mail servers, especially Gmail, is a frequent cause of delivery issues, indicating that sending volume or velocity might be too high for the current sender reputation.
- Integration complexity: Setting up custom SMTP or integrating two platforms can introduce complexities that lead to data syncing issues, affecting how delivery metrics are reported across systems.
Key considerations
- Check SendGrid suppressions: Always review the bounce and block lists in SendGrid to understand if recipients are being intentionally suppressed due to prior issues, which can drastically reduce perceived delivery rates.
- Monitor domain health: Even with a good ESP, your domain's reputation is paramount. Pay attention to engagement metrics and avoid practices that could lead to domain blocklisting or poor sender reputation.
- Segment sending: If experiencing rate limiting, consider segmenting your sends or spreading them out over a longer period to avoid overwhelming recipient servers.
- Troubleshoot integration: If SendGrid shows higher delivery rates than Customer.io, investigate the integration data flow to ensure metrics are being correctly reported back to Customer.io. This is a common cause for reported delivery discrepancies.
Marketer view
Email marketer from Email Geeks indicates they were seeing very low delivery rates (20%) through Customer.io when using SendGrid, particularly for Gmail recipients. They noted that Customer.io's bounce and failed reports were not providing enough useful information to understand the problem. This suggests a common pain point for marketers: the disconnect between an ESP's reported delivery status and actual inbox placement, or even a lack of detailed bounce reasons within the marketing automation platform.
Marketer view
Email marketer from Email Geeks mentions that SendGrid's own metrics showed 50% delivered requests, highlighting a discrepancy between Customer.io's 20% delivery and SendGrid's numbers. They were initially unfamiliar with how to access SendGrid's SMTP logs to investigate further. This points to the need for marketers to gain proficiency in navigating their ESP's analytics and diagnostic tools to properly troubleshoot delivery issues, even when using a third-party platform.
What the experts say
Experts emphasize a systematic approach to diagnosing deliverability issues when using Customer.io with SendGrid. They highlight that while Customer.io provides a user-friendly interface for campaigns, the underlying email delivery complexities often require consulting the ESP's (SendGrid's) detailed logs. The consensus points to verifying integration setups, understanding bounce feedback, and maintaining a robust sender reputation to ensure emails reach the inbox.
Key opinions
- Direct support is best: When issues persist, particularly with custom SMTP configurations, directly engaging the deliverability support team of the platform (e.g., Customer.io's deliverability services manager) is the most efficient path to resolution.
- SMTP logs provide the truth: The raw SMTP logs from SendGrid are the definitive source of truth for understanding delivery attempts, responses from receiving servers, and ultimate delivery or failure outcomes.
- Bounce analysis is critical: Understanding specific bounce reasons, whether soft or hard, transient or permanent, is crucial for refining sending practices and list hygiene.
- Sender reputation impacts all mail: Even with legitimate mail, a poor sender reputation (often influenced by previous spam complaints or high bounce rates) can lead to blocks or emails landing in spam folders, as detailed in our guide on why emails go to spam.
- Authentication is foundational: Properly configured SPF, DKIM, and DMARC records are fundamental to establishing trust with mailbox providers and ensuring your emails are not flagged as suspicious. Learn more in our simple guide to email authentication.
Key considerations
- Proactive monitoring: Don't wait for delivery rates to plummet. Proactively monitor your domain and IP reputation using tools like Google Postmaster Tools for Gmail specific insights, which helps in improving domain reputation.
- List hygiene: Regularly clean your email lists to remove inactive or bouncing addresses. Sending to invalid addresses can quickly degrade your sender reputation and lead to blacklisting.
- Content quality: Even with perfect technical setup, spammy content, broken links, or misleading subject lines can trigger filters. Ensure your email content is relevant and provides value.
- Handle blocks and suppressions: Understand the difference between temporary blocks and permanent suppressions. Address the root cause of blocks and ensure permanent bounces are removed from your sending lists.
Expert view
Deliverability Services Manager from Email Geeks suggests that if you are using SendGrid via Custom SMTP with Customer.io, reaching out to their support team directly (win@customer.io) is recommended for a thorough investigation of delivery issues. This highlights that complex integrations often require specialized support from the platform vendor to diagnose and resolve unique deliverability challenges, especially when dealing with custom setups.
Expert view
Expert from SpamResource emphasizes that email authentication (SPF, DKIM, DMARC) is non-negotiable for deliverability. If these records are misconfigured or missing, even legitimate emails will struggle to reach the inbox and may be routed to spam folders or rejected outright. Proper authentication builds trust with mailbox providers, signaling that your emails are legitimate and not spoofed, which is a foundational element of good sending practices.
What the documentation says
Official documentation from both Customer.io and SendGrid provides clear guidance on setting up integrations and troubleshooting common issues. It emphasizes that while Customer.io offers its own email delivery, users can leverage existing SendGrid accounts via custom SMTP. The documentation outlines best practices for email deliverability, the meaning of failed messages, and how to access logs and troubleshooting tools. It consistently points to proper setup and adherence to best practices as key to successful email delivery.
Key findings
- Flexible sending options: Customer.io allows users to either deliver email through its own service or use an existing account with another provider like SendGrid, providing flexibility but requiring careful setup.
- Definition of failed messages: A failed message in Customer.io means it never successfully left the platform to the delivery provider, indicating an internal issue before external sending.
- Importance of proper setup: To fully utilize SendGrid through Customer.io, users need to correctly configure their SendGrid account details within Customer.io.
- Email deliverability best practices: Customer.io strongly advises practices like double opt-in to verify email addresses before sending, which is crucial for maintaining sender reputation.
- Post-delivery filtering: Even if an email is reported as delivered by the ESP, the recipient server might still sort it into a spam folder or other tabs (e.g., Gmail's Promotions tab).
Key considerations
- Review campaign settings: Check if campaigns or API-triggered broadcasts are set to queue messages rather than send automatically within Customer.io, as this can affect perceived delivery times.
- Utilize ESP's troubleshooting: When using SendGrid as your delivery provider, rely on its activity logs and suppression lists for the most accurate and detailed information on email statuses and reasons for non-delivery.
- Adhere to best practices: Follow Customer.io's recommended email deliverability best practices, such as verifying addresses and ensuring list quality, to prevent bounces and maintain a good sender reputation.
- Troubleshoot integration errors: If messages are failing to leave Customer.io (even before reaching SendGrid), consult Customer.io's troubleshooting guides for integrations to identify API or setup issues.
Technical article
Customer.io documentation states that users can either send email through Customer.io's default delivery or integrate their existing SendGrid account. When using SendGrid, there is no loss in functionality from Customer.io's side, suggesting that core features remain available. This highlights the flexibility offered but implies that deliverability management then largely shifts to the SendGrid platform.
Technical article
Customer.io documentation explains that a failed message means it was not successfully sent to the delivery provider and therefore never left Customer.io. This indicates that troubleshooting should begin within Customer.io itself if messages are marked as failed. This crucial distinction helps identify whether the problem lies within Customer.io's processing or with the external ESP (SendGrid).
Related resources
8 resources
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