Summary
The SMTP bounce reason 4.1.8, 'bad sender's system address, domain of sender address does not resolve,' indicates that the recipient's mail server is unable to resolve the sender's domain. This resolution failure is commonly attributed to a range of DNS-related problems, encompassing misconfigured DNS records (A, MX, SPF, DKIM), transient DNS failures or outages, DNS propagation delays after updates, or even sender domain reputation issues leading to rejection. Initially, a 4.1.8 error manifests as a deferral, suggesting retries, but persistent occurrences signal the need to investigate and address underlying DNS or reputation problems.
Key findings
- DNS Resolution Failure: The primary issue is the recipient server's inability to resolve the sender's domain.
- DNS Configuration Problems: Misconfigured DNS records (A, MX, SPF, DKIM) are a common cause.
- Transient DNS Issues: Temporary DNS failures or propagation delays can trigger this error, often leading to initial deferrals.
- Sender Reputation Impact: A poor sender domain reputation can lead to recipient servers rejecting emails with this bounce code.
- Error as Deferral: The 4.1.8 error initially presents as a deferral, indicating that retries are expected, but persistent errors suggest a more serious issue.
Key considerations
- Check DNS Records: Verify that A, MX, SPF, and DKIM records are correctly configured and publicly accessible.
- Account for DNS Propagation: Allow 24-48 hours for DNS changes to propagate fully after updates.
- Monitor Sender Reputation: Check sender domain reputation and address any issues that may be negatively impacting deliverability.
- Monitor for Persistent Errors: While initial 4.1.8 errors can be transient, continuous occurrences warrant further investigation.
- Address Potential DNS Outages: Rule out temporary DNS server problems causing the resolution failure.
What email marketers say
9 marketer opinions
An SMTP bounce reason 4.1.8, 'bad sender's system address, domain of sender address does not resolve,' indicates the receiving server is unable to resolve the sender's domain. This can be due to various DNS-related issues, including misconfigured DNS records (A, MX, SPF, DKIM), DNS propagation delays after updates, temporary DNS server outages, or even sender domain reputation issues that cause recipient servers to reject the emails. Transient failures are common and retries are suggested, although checking underlying DNS issues is also important.
Key opinions
- DNS Resolution Failure: The primary cause is the recipient server's inability to resolve the sender's domain.
- DNS Configuration: Incorrectly configured DNS records (A, MX, SPF, DKIM) are a frequent culprit.
- Temporary DNS Issues: Transient DNS server outages or propagation delays after DNS updates can trigger this error.
- Reputation Impact: A poor sender domain reputation can lead recipient servers to reject emails, resulting in a 4.1.8 bounce.
Key considerations
- Check DNS Records: Verify that A, MX, SPF, and DKIM records are correctly configured for the sending domain.
- DNS Propagation: Allow sufficient time (24-48 hours) for DNS changes to propagate fully after making updates.
- Monitor Reputation: Check sender domain reputation and address any issues that may negatively impact it.
- Retry Sending: For transient DNS failures, retrying the email send may resolve the issue.
Marketer view
Email marketer from SparkPost shares that a 4.1.8 status code often indicates a transient DNS failure and retries are recommended, but may require more urgent attention if it doesn't resolve quickly.
14 Sep 2022 - SparkPost
Marketer view
Email marketer from Postmark shares that while less common, 4.1.8 errors *could* potentially be related to DKIM issues if the recipient server is particularly strict. They recommend verifying the DKIM signature for outbound emails.
6 Jul 2021 - Postmark
What the experts say
3 expert opinions
An SMTP bounce reason 4.1.8, indicating a 'bad sender's system address' because the domain of the sender address does not resolve, suggests a problem where the receiving server is unable to find the sender's domain. This can stem from DNS configuration issues, temporary outages, or sender reputation problems. A 4xx error initially represents a deferral and retries are expected, but if it escalates, it could signify more severe problems.
Key opinions
- Domain Resolution Failure: The receiving server cannot resolve the sender's domain name, which leads to the bounce.
- Potential Causes: DNS configuration problems, temporary DNS outages, and sender reputation issues are potential causes.
- Deferral vs. Rejection: A 4.1.8 error initially manifests as a deferral (4xx code), and deliveries are typically retried. Persistent issues can lead to a permanent rejection.
Key considerations
- Check DNS Configuration: Ensure DNS records are correctly set up and resolve properly.
- Monitor for Escalation: While initial 4.1.8 errors can be transient, monitor them to ensure they don't escalate to permanent rejections.
- Assess Sender Reputation: Investigate if the sender domain's reputation is negatively impacting deliverability.
Expert view
Expert from SpamResource explains that a 4.1.8 bounce often indicates that the receiving server could not resolve the sender's domain name. This is frequently caused by DNS configuration problems or a temporary outage.
16 Apr 2024 - SpamResource
Expert view
Expert from Email Geeks explains that 4xx is a deferral, not a bounce, and is a very normal response to transient DNS failures. Deliveries will be retried and can be ignored unless escalated to a rejection after a number of deferrals.
15 Sep 2022 - Email Geeks
What the documentation says
4 technical articles
The SMTP bounce reason 4.1.8, 'bad sender's system address, domain of sender address does not resolve,' signals that the recipient mail server is unable to resolve the domain of the sender. This is typically caused by DNS issues, including misconfigured DNS records, temporary DNS server problems, or an incorrect domain syntax. While transient issues might exist, this error often points to a more fundamental problem with the sender's domain configuration.
Key findings
- Domain Resolution Problem: The primary issue is the recipient's mail server failing to resolve the sender's domain.
- DNS Related: The root cause is usually related to DNS, including misconfiguration or temporary DNS outages.
- Incorrect Syntax: The sender address or domain might be syntactically incorrect according to RFC standards.
Key considerations
- Verify DNS Configuration: Ensure that all DNS records are correctly configured and publicly accessible.
- Check for Syntax Errors: Examine the sender address and domain for any syntax errors that might prevent resolution.
- Investigate DNS Outages: Rule out any temporary DNS server problems causing the resolution failure.
Technical article
Documentation from RFC Editor details that 4.1.8 enhanced status code indicates a 'bad sender's system address'. The domain name does not resolve, or the address is syntactically incorrect. (this is a permanent error).
28 Apr 2025 - RFC 3463
Technical article
Documentation from Microsoft Docs explains that SMTP error code 4.1.8 indicates a problem with the sender's domain name resolution. It usually means the recipient's mail server was unable to resolve the sender's domain, which could be due to DNS issues or a misconfigured domain.
19 Feb 2023 - Microsoft Docs
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