Summary
A TempFail, suspected as spam, represents a temporary email delivery issue with varied causes. These range from recipient server problems (unavailability, overload), greylisting (temporary rejection of unknown senders), exceeding sending limits, to issues with sender reputation and email authentication. Troubleshooting starts with examining actual bounce messages, not just ESP classifications, and implementing retry logic. Key strategies involve verifying sender reputation by checking IP addresses against blacklists, ensuring proper authentication (SPF, DKIM, DMARC), maintaining a clean email list (removing inactive subscribers, validating addresses), and monitoring feedback loops. Messages classified as '[internal]' are suppressed by the MTA, while 'No MX or A' means an invalid domain. Addressing these temporary failures requires a multi-faceted approach to ensure proper delivery and avoid permanent bounces. Soft bounces indicate temporary issues while hard bounces are permanent.
Key findings
- Transient Errors: TempFails are transient errors indicated by 4xx SMTP codes.
- Multiple Causes: They arise from various factors, including server issues, greylisting, sending limits, and reputation problems.
- Authentication Crucial: Proper SPF, DKIM, and DMARC authentication is vital to avoid being flagged as spam.
- List Hygiene Important: Maintaining a clean email list reduces the likelihood of hitting spam traps and triggering TempFails.
- ESP Data Questionable: Relying solely on ESP bounce classifications can be misleading; examine raw bounce data.
Key considerations
- Examine Bounce Messages: Review actual deferral/bounce messages directly from the ISP, not just ESP summaries.
- Retry Delivery: Implement retry logic for failed deliveries, as the problem might be temporary.
- Monitor Feedback Loops: Actively monitor feedback loops to identify and address deliverability issues.
- Manage Sender Reputation: Proactively manage sender reputation to minimize the risk of being marked as spam.
- Server Status Check: Ensure the recipient's server is operational and accepting emails.
What email marketers say
8 marketer opinions
A TempFail, or temporary failure, in email delivery often indicates a transient issue such as recipient server unavailability, greylisting (a spam prevention technique), or exceeding sending limits. Troubleshooting involves checking server status, monitoring bounce codes, adjusting sending frequency, ensuring proper authentication (SPF, DKIM), and maintaining a clean email list by removing inactive subscribers and validating email addresses. Maintaining a good sender reputation is crucial to avoid being flagged as spam, which can also lead to TempFails. If the issue persists, contacting the recipient's email provider might be necessary. Proper email authentication prevents emails being marked as spam. Emails with TempFail errors might be categorized as soft bounces
Key opinions
- Temporary Issue: TempFails indicate temporary issues preventing email delivery, as opposed to permanent failures.
- Greylisting: Greylisting, a spam prevention technique, commonly causes TempFails.
- Authentication: Proper email authentication (SPF, DKIM) is essential to avoid being flagged as spam and encountering TempFails. Emails marked as spam are likely to bounce.
- Sender Reputation: Maintaining a good sender reputation is crucial to prevent spam flagging and TempFails.
- Soft Bounces: Emails that result in TempFail errors might be categorized as soft bounces which are temporary issues in email delivery.
Key considerations
- Troubleshooting: Check server status, monitor bounce codes, and adjust sending frequency to resolve TempFails.
- Retry Sending: Resend emails after a delay, as the issue might be temporary.
- List Hygiene: Maintain a clean email list by removing inactive subscribers and validating email addresses.
- Persistent Issues: If TempFails persist, investigate sender reputation or contact the recipient's email provider.
- Bounce Categories: Fix bounces, both soft and hard to ensure proper email delivery
Marketer view
Email marketer from StackOverflow explains that emails bounce with TempFail because of issues like server overload, greylisting, or recipient mailbox issues. The email server will automatically retry sending the email and if it continues, it can become a permanent error.
3 Dec 2023 - StackOverflow
Marketer view
Email marketer from DigitalOcean explains that it is essential to implement SPF and DKIM authentication to prevent emails being marked as spam. Without proper authentication, your emails are more likely to bounce and this includes getting a TempFail error.
25 Feb 2025 - DigitalOcean
What the experts say
7 expert opinions
A TempFail, often flagged as suspected spam, can stem from several underlying issues. It's crucial to examine the actual deferral messages from the ISP, rather than relying solely on ESP classifications, which can be inaccurate. Issues can range from bad email addresses and poor sender reputation to greylisting, where receiving servers temporarily reject emails from unknown senders. Messages marked '[internal]' indicate suppression by the MTA, while 'No MX or A' suggests an invalid domain. Proper authentication (SPF, DKIM, DMARC) and monitoring feedback loops are vital for maintaining a good reputation. Additionally, some '[internal]' messages are escalations from repeated 4xx deferrals, leading to synthetic 5xx rejections.
Key opinions
- ESP Inaccuracy: ESPs' classification of bounce messages can be inaccurate; obtaining the actual deferral messages is crucial.
- Bad Email Addresses: TempFails can indicate bad email addresses, necessitating review of acquisition sources and bounce management processes.
- Internal Messages: Messages marked '[internal]' signify suppression by the MTA, while 'No MX or A' means an invalid domain.
- Greylisting Cause: Greylisting is a common cause of temporary failures, especially from unknown senders.
- Reputation Impact: Poor sender reputation can lead to TempFails, emphasizing the importance of proper authentication and avoiding unsolicited emails.
Key considerations
- Message Examination: Examine actual deferral messages from the ISP to accurately diagnose the issue.
- Source Verification: Verify the source of recently acquired email addresses and review bounce management processes.
- Authentication: Ensure proper authentication (SPF, DKIM, DMARC) to maintain a positive sender reputation.
- Feedback Monitoring: Monitor feedback loops to identify and address issues affecting sender reputation.
- Differentiate Issues: Differentiate greylisting from other issues through careful monitoring of delivery attempts and bounce messages.
Expert view
Expert from Email Geeks explains that messages containing '[internal]' indicate suppression by the MTA without attempted delivery, while 'No MX or A' signifies an invalid domain.
19 Jan 2023 - Email Geeks
Expert view
Expert from Email Geeks recommends obtaining the actual deferral messages from the ESP to understand the issue, as the ESP's classification may be inaccurate. He suggests the deferrals might be temporary and the deliveries will be retried, but it could also be an early warning sign.
3 Jan 2023 - Email Geeks
What the documentation says
4 technical articles
A TempFail, also known as a transient error, signifies a temporary obstacle to email delivery. These errors are typically indicated by 4xx SMTP error codes and suggest that the sending system may be able to resend the message with success. Common causes include server overload, temporary unavailability, or greylisting. Troubleshooting involves verifying sender reputation, ensuring proper authentication (SPF, DKIM, DMARC), checking IP address against blacklists, and confirming the recipient's server is operational. Implementing retry logic in applications is necessary to handle these transient errors, as repeated failures may lead to the email being treated as a bounce.
Key findings
- Transient Nature: TempFails are transient errors, indicating temporary issues rather than permanent delivery failures.
- SMTP Codes: 4xx SMTP error codes commonly signify TempFails.
- Retry Logic: Applications must implement retry logic to handle transient errors effectively.
Key considerations
- Reputation: Verify sender reputation to ensure it is not the cause of delivery issues.
- Authentication: Ensure proper authentication (SPF, DKIM, DMARC) is in place to prevent emails from being flagged as spam.
- Blacklist Check: Check IP addresses against blacklists to identify potential reputation problems.
- Server Status: Confirm the recipient's server is operational and accepting mail.
- Error Logs: Check server logs for detailed error messages to understand the specific cause of the TempFail.
Technical article
Documentation from Amazon Web Services explains that transient email delivery errors require you to implement logic in your applications to retry sending those emails. If the same email encounters repeat transient errors, it may be treated as a bounce.
18 Sep 2023 - Amazon Web Services
Technical article
Documentation from Google Workspace Admin Help explains that a 4xx SMTP error code typically indicates a temporary failure. This can be due to server overload, temporary unavailability, or greylisting. They recommend checking server logs for detailed error messages and retrying sending the email after a delay.
14 Apr 2025 - Google Workspace Admin Help
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