How do I troubleshoot delivery errors and TempFail messages in Klaviyo when using Gmail?
Matthew Whittaker
Co-founder & CTO, Suped
Published 24 Jun 2025
Updated 13 Oct 2025
6 min read
Encountering delivery errors and TempFail messages in Klaviyo when sending to Gmail can be a frustrating experience. Even with a robust DMARC policy set to quarantine and high authentication rates, these temporary rejections can still impact your email performance. The key to resolving these issues lies in a systematic approach, diving deep into diagnostics and understanding the nuances of Gmail's filtering mechanisms. It's often not a simple fix, but a process of careful investigation and adjustment across various aspects of your email sending.
Decoding Gmail's TempFail messages
A TempFail message from Gmail indicates a temporary rejection of your email. Unlike a hard bounce, which signifies a permanent failure, a TempFail suggests that the email server might accept the message later. Common reasons include suspected spam, a temporary issue with the recipient's mailbox, or rate limiting applied by Gmail due to sending volume or reputation concerns.
When Gmail suspects a message is spam, it might issue a 421 4.7.0 error code, indicating that the message is suspicious due to low sender or domain reputation. This type of rejection is often tied to content analysis, sending patterns, or even specific URLs within the email that have been previously flagged. It's a signal that Gmail needs more assurance of your legitimacy before accepting the email.
Another common TempFail reason is a mailbox full error. While less indicative of a reputation problem, it still impacts delivery. These are typically self-correcting as recipients clear space, but a high volume can suggest an unengaged list. It's crucial to understand these distinctions to focus your troubleshooting efforts effectively.
Understanding Gmail's temporary rejections
Gmail's TempFail (4xx) errors are temporary and often retried by the sending server. However, persistent TempFails can indicate underlying issues that need attention.
Reputation-based:Often signals suspected spam due to low sender reputation, content issues, or unusual sending patterns.
Resource-based:Includes mailbox full or too many mails messages. These often clear up on their own.
Pinpointing the source of Klaviyo delivery issues
The first step in troubleshooting is to ascertain whether the delivery errors are originating from Klaviyo. While Klaviyo's logs might show a 250 status code (delivered), this doesn't guarantee inbox placement, only successful handover. You need to look closer at the bounce details within Klaviyo itself.
Access your Klaviyo bounce logs and filter for Gmail addresses. Many platforms, including Klaviyo, provide metadata (often in JSON format) alongside bounce notifications that can offer specific reasons for a temporary rejection. This data is invaluable for understanding the exact nature of the TempFail.
If you're using a shared IP address in Klaviyo, direct access to raw mail logs (where you might use a command like grep for gsmtp errors) is usually unavailable. In such cases, your best bet is to rely on the detailed bounce reports provided by Klaviyo or escalate the issue to their support team for deeper investigation.
Example of searching mail logs (for dedicated IPs)BASH
grep 'gsmtp' /var/log/mail.log | grep 'TempFail'
Addressing common causes behind TempFail messages
Once you've confirmed that the TempFails are indeed occurring from Klaviyo-sent emails, you can investigate the common culprits. For suspected spam errors, the issue often boils down to sender reputation or specific content. Gmail is highly sensitive to these factors. This could mean your domain reputation has taken a hit, or the shared IP you're using might have a poorer reputation from other senders.
Content is another major factor. Are there particular links, images, or keywords in your emails that might be triggering spam filters? Sometimes, even legitimate link tracking tools can inadvertently be flagged if they've been abused by other senders. Examine recent campaigns for any changes in content, sending volume, or audience segmentation that might correlate with the rise in TempFails.
For mailbox full messages, while they are temporary, a high occurrence suggests that your list might contain inactive or outdated addresses. Regularly cleaning your list and removing unengaged subscribers can mitigate these issues and improve overall deliverability. Ensure your exclusion lists are updated to prevent sending to known problematic addresses.
Content and reputation issues
Review email content: Scan for spammy keywords, excessive images, or poor HTML formatting.
Check links: Ensure all URLs are legitimate and not blocklisted or associated with past spam complaints.
Monitor sender reputation: Use Google Postmaster Tools to track your domain's health and spam rates.
Recipient-side and list hygiene
Segment by bounce reason: Isolate recipients frequently hitting mailbox full errors and consider segmenting them out temporarily or removing them.
List cleaning: Implement a regular list hygiene strategy to remove inactive or problematic email addresses.
Engagement monitoring: Focus on sending to engaged subscribers to improve overall deliverability and reduce complaint rates.
Leveraging email authentication and monitoring for prevention
While a DMARC p=quarantine policy with 99.7% authentication is excellent for email authentication, it's typically not the direct cause of TempFail messages. These authentication protocols primarily prevent spoofing and ensure legitimate senders. However, DMARC reports provide a holistic view of your email ecosystem, which can indirectly help in troubleshooting.
Using a DMARC monitoring tool like Suped allows you to see all sources sending email on behalf of your domain. This can help identify unauthorized senders that might be damaging your reputation, even if they aren't using Klaviyo. Regular review of these reports can highlight areas where authentication might be failing for other streams, which could contribute to overall domain reputation issues.
In addition to DMARC, consider blocklist monitoring to ensure your sending IP (if dedicated) or domain isn't listed, which could cause TempFails. Although Klaviyo manages shared IPs, monitoring your domain's blocklist (or blacklist) status is a good practice for comprehensive deliverability health.
Proactive email health monitoring
DMARC reports: Utilize Suped's DMARC monitoring to gain visibility into all email sending sources and their authentication status.
Regular audits: Periodically audit your Klaviyo setup, content, and list hygiene practices. Ensure your email deliverability tests are up to date.
Maintain engagement: A highly engaged audience sends positive signals to ISPs, improving your reputation and reducing TempFails.
Views from the trenches
Best practices
Actively monitor Klaviyo's bounce logs, specifically for Gmail addresses, to identify exact TempFail reasons.
Regularly segment and clean your email lists to remove unengaged subscribers and addresses prone to mailbox full errors.
Carefully review email content, including all links, for anything that could trigger spam filters or indicate low sender reputation.
Leverage DMARC reports from tools like Suped to get a comprehensive view of all email sending sources for your domain.
Common pitfalls
Assuming good DMARC authentication (p=quarantine) means immunity from all delivery issues, especially TempFails.
Overlooking subtle changes in email content or tracking links that could negatively impact sender reputation with Gmail.
Not differentiating between 'suspected spam' TempFails and 'mailbox full' TempFails, leading to misdirected troubleshooting.
Failing to engage with Klaviyo support for deeper log analysis when direct access to raw logs is unavailable.
Expert tips
When on a shared IP, specific log searching like 'grep' isn't possible, so rely heavily on your ESP's detailed bounce analytics.
If TempFails happen before the DATA command in SMTP, it's about IP/domain reputation or recipient issues, not content.
If TempFails happen after the DATA command, inspect email content, especially links, as they are likely the cause.
Don't solely rely on open rates; actively monitor Postmaster Tools and DMARC reports for true deliverability insights.
Marketer view
Marketer from Email Geeks says: I noticed a lot of TempFail messages for my client even with a strong DMARC policy. I'm struggling to identify the specific sources.
2023-04-07 - Email Geeks
Expert view
Expert from Email Geeks says: Delivery errors are typically visible in your delivery logs. You should dig through those logs to find what mail Google is rejecting, focusing on specific Google errors, and then address the issues as indicated by the log messages.
2023-04-07 - Email Geeks
Conclusion
Troubleshooting delivery errors and TempFail messages in Klaviyo for Gmail requires a methodical approach. It involves scrutinizing Klaviyo's internal bounce data, understanding the implications of different TempFail types, and meticulously examining your email content and sending practices. While DMARC provides a strong foundation for authentication, continuous DMARC monitoring with tools like Suped offers crucial visibility into your entire email sending ecosystem. By combining internal platform data with broader email security insights, you can effectively diagnose and resolve delivery challenges, ensuring your messages consistently reach the inbox.
