Suped

Why am I getting a Yahoo error 451 due to an unresolvable RFC 5321 domain?

6 Marketer opinions2 Expert opinions3 Technical articles4 Resources

Summary

A Yahoo error 451, triggered by an unresolvable RFC 5321 domain, indicates a temporary email delivery issue with multiple potential causes. Primary among these are DNS misconfigurations: broken DNS for the MAIL FROM domain, nameservers refusing queries, missing SOA records, or incorrect delegation of subdomains. Temporary server issues such as greylisting, spam filtering delays (especially in Postfix), and general DNS resolution problems between sender and recipient can also trigger this error. Resolving this often requires verifying and correcting DNS records with your domain registrar, ensuring proper DNS resolution, retrying the email send, and, in some cases, adjusting spam filter settings. Diagnostic tools like MXToolbox can aid in pinpointing DNS-related problems.

Key findings

  • DNS Issues: Broken DNS, missing SOA records, or misconfigured nameservers for the MAIL FROM domain are frequent causes.
  • Temporary Server Problems: Greylisting, spam filtering issues, and DNS resolution problems on the receiving server can lead to 451 errors.
  • Postfix Specifics: In Postfix environments, slow spam filters might cause timeouts resulting in 451 errors.
  • General Configuration: Incorrect delegation and improperly configured DNS records can cause the 451 error.

Key considerations

  • Retry Sending: Attempt to resend the email as the error is often temporary.
  • Verify DNS: Thoroughly check and correct DNS records, including SOA and A records, with your domain registrar.
  • Check DNS Resolution: Ensure the sending server can resolve external domains to rule out resolution issues.
  • Postfix Settings: For Postfix users, adjust spam filter timeout settings.
  • Use Diagnostic Tools: Utilize tools like MXToolbox to diagnose DNS problems.
  • Correct Delegation: Ensure correct delegation practices for subdomains avoiding incorrect setups.

What email marketers say
6Marketer opinions

A Yahoo error 451, related to an unresolvable RFC 5321 domain, typically signifies a temporary issue preventing email delivery. Several factors can contribute, including DNS misconfiguration on the sender's side, temporary problems on the receiving server (like greylisting), slow spam filters in Postfix, or general DNS resolution issues. Resolving this error often involves checking and correcting DNS records, ensuring the sender's server can resolve external domains, and potentially adjusting spam filter settings. Retrying the email send is also a recommended initial step.

Key opinions

  • DNS Configuration: Incorrect or missing DNS records for the domain used in the MAIL FROM command are a common cause.
  • Temporary Server Issues: The receiving server may be experiencing temporary problems like greylisting or other transient issues.
  • Postfix Spam Filters: In Postfix environments, slow spam filters can trigger 451 errors; adjusting timeout settings may help.
  • DNS Resolution: Temporary DNS resolution issues between the sender and recipient servers can lead to this error.

Key considerations

  • Retry Sending: As the error is temporary, retrying the email send is a crucial first step.
  • Check DNS Records: Thoroughly verify and correct DNS records, including SOA and A records, for the sending domain.
  • Verify DNS Resolution: Ensure the sending server can resolve external domains to rule out resolution issues.
  • Adjust Spam Filter Settings: If using Postfix, consider adjusting timeout settings for spam filters to prevent delays.
  • Diagnose with MXToolbox: Use tools like MXToolbox to diagnose and identify potential DNS-related problems.
Marketer view

Email marketer from EmailOnAcid explains that a 4xx error like 451 means a temporary issue and the sender should attempt to resend, and suggests investigating DNS and server settings, but retry first.

July 2024 - EmailOnAcid
Marketer view

Email marketer from Stack Overflow answers that in Postfix the error might relate to spam filters running slowly so try adjusting the 'timeout' for the filters.

January 2025 - Stack Overflow
Marketer view

Email marketer from Reddit shares that a 451 error could be due to DNS issues on the sender's side, especially if the domain in the MAIL FROM command lacks proper DNS records or the nameservers are not responding correctly.

December 2024 - Reddit
Marketer view

Email marketer from cPanel Forum shares that the error indicates that there may be temporary DNS resolution issues between your server and the recipient's server. Ensure your DNS records are correctly configured and that your server can resolve external domains.

February 2024 - cPanel Forum
Marketer view

Email marketer from MailerQ Blog shares that a 451 error often means the receiving server has a temporary problem, like DNS issues, greylisting, or other transient issues. The server is temporarily refusing to accept the email and retries are usually successful.

September 2021 - MailerQ Blog
Marketer view

Email marketer from MXToolbox shares that the 451 error points to issues in DNS configuration, meaning the domain used in the MAIL FROM command might not have properly configured DNS records or the DNS servers aren't responding correctly. They recommended using MXToolbox to diagnose the DNS.

July 2023 - MXToolbox

What the experts say
2Expert opinions

A Yahoo error 451, specifically related to an unresolvable RFC 5321 domain, is often caused by DNS configuration problems. The primary domain may be misconfigured, causing DNS servers to refuse queries and making the domain appear non-existent to Yahoo. This can occur when customers incorrectly delegate subdomains instead of properly setting up nameservers for the main domain. Resolution involves verifying and correcting DNS settings with your domain registrar, ensuring the MAIL FROM domain resolves correctly and checking for DNS server errors.

Key opinions

  • Broken DNS: The DNS for the bounce domain is broken, preventing Yahoo from resolving the domain.
  • Nameserver Refusal: Nameservers for the primary domain refuse to answer queries, causing the domain to appear non-existent.
  • Incorrect Delegation: Customers may have incorrectly delegated subdomains instead of properly configuring nameservers for the main domain.
  • General DNS Misconfiguration: The Yahoo error 451 often indicates an issue with general DNS configuration.

Key considerations

  • Correct DNS Setup: Verify and correct DNS settings with your domain registrar.
  • Ensure Resolution: Ensure that the domain used in the MAIL FROM command resolves correctly.
  • Check DNS Records: Check the SOA record and A records for the affected domain and subdomains.
  • Proper Nameserver Setup: Ensure proper configuration of nameservers for the main domain, avoiding incorrect subdomain delegation.
Expert view

Expert from Email Geeks explains that the DNS for bounce.email.marketcarpenter.com is broken, causing Yahoo's error 451. The nameservers for marketcarpenter.com refuse to answer queries, making the domain appear non-existent to Yahoo. This occurs because customers likely delegated email.marketcarpenter.com instead of properly configuring the nameservers for marketcarpenter.com.

June 2024 - Email Geeks
Expert view

Expert from Word to the Wise explains that the Yahoo error 451 often indicates an issue with DNS configuration. Ensure that the domain used in the MAIL FROM command resolves correctly and that there are no DNS server errors. Check the SOA record, and A records for the affected domain and subdomains. This type of DNS error should be resolved by confirming and correcting the setup with your domain registrar.

May 2024 - Word to the Wise

What the documentation says
3Technical articles

A Yahoo error 451, related to an unresolvable RFC 5321 domain, signifies a temporary deferral. According to Yahoo Postmaster, this can stem from a missing Start of Authority (SOA) record for the subdomain, particularly when multiple addresses are used in the MAIL FROM command, emphasizing the need for correct DNS setup. RFC 5321 clarifies it as a generic server error prompting retries. The Exim Wiki adds that greylisting, spam filtering, or resource constraints on the recipient's end can also trigger these errors.

Key findings

  • SOA Record Missing: Lack of a Start of Authority (SOA) record for the subdomain in the MAIL FROM command can cause Yahoo's 451 error.
  • Generic Server Error: RFC 5321 defines the 451 error as a general server-side issue, recommending retrying the email transaction.
  • Recipient-Side Issues: Greylisting, spam filtering, or temporary resource unavailability on the recipient server can also generate 451 errors, as highlighted by the Exim Wiki.

Key considerations

  • Verify DNS Configuration: Ensure proper DNS configuration, especially the presence of an SOA record, for the sending domain as per Yahoo's recommendation.
  • Retry Sending: As the error indicates a temporary issue, retry sending the email at a later time.
  • Investigate Recipient Issues: Consider the possibility of greylisting or other recipient-side issues if the error persists despite correct DNS configuration.
Technical article

Documentation from Exim Wiki explains that 451 errors can also be generated by the receiving server due to greylisting (delaying acceptance from unknown senders), spam filtering issues, or temporary unavailability of resources.

November 2023 - Exim Wiki
Technical article

Documentation from RFC 5321 explains that a 451 SMTP error code indicates that the requested action was aborted due to some server error. The mail transaction may be tried again later.

October 2021 - RFC Editor
Technical article

Documentation from Yahoo Postmaster explains that the 451 error code indicates a temporary deferral due to an unresolvable RFC 5321 domain, which could be caused by the lack of a Start of Authority (SOA) record for the subdomain if more than one address is used in the MAIL FROM command. Yahoo suggests ensuring proper DNS configuration for the sending domain.

February 2022 - Yahoo Postmaster

Related resources
4Resources

Unresolvable RFC.5321 domain at Yahoo – Word to the Wise
Unresolvable RFC.5321 domain at Yahoo – Word to the Wise

Seen this recently? 451 Message temporarily deferred due to unresolvable RFC.5321 from domain; see This is Yahoo doing some extra work to identify that the 5321.From domainThe return-path, aka the …

Word to the Wise
SOA records for subdomains? - DNS & Network - Cloudflare ...
SOA records for subdomains? - DNS & Network - Cloudflare ...

I apologize, since I’m a new community forums user it doesn’t look like it’s allowing me to post links in this post. I searched the Community Forums for an answer, and didn’t find anything specific to this. I run a community organization with domains the organization reserved a few years ago, and just recently launched a new site on one of these domains, with all other domains pointing to the .org domain. Currently, I use my VPS provider’s DNS to manage this domain. As part of the new site r...

Cloudflare Community
I am still having problems sending Yahoo emails to recipents ...
I am still having problems sending Yahoo emails to recipents ...

Troubleshooting Yahoo Email Sending Issues: Expert Q&A

JustAnswer
Yahoo temporarily deferred due to user complaints - Collaboration ...
Yahoo temporarily deferred due to user complaints - Collaboration ...

Hi, We have our own Exchange server 2016. We’ve encountered this issue “Temporarily deferred due to user complaints” from Yahoo!. This issue occurs only for those yahoo users. Its been months now and we are still having an issue with Yahoo users. Any way to solve this? Regards,

Spiceworks Community

Related questions