Loading

Salesforce Email Deliverability Fails Due to DNS Standards Non-Compliance (Error 421 4.4.0 / 554 5.4.4)

Publiseringsdato: May 5, 2026
Beskrivelse

Salesforce email delivery may fail when the recipient's DNS infrastructure does not comply with current DNS standards. Users notice that emails sent from Salesforce go undelivered to certain customers or co-workers, even though the same emails deliver successfully from other senders or from the corporate email server.


Email logs show one or both of the following error messages:

  • 421 4.4.0 [internal] no mail servers for this domain could be reached at this time
  • 554 5.4.4 [internal] Domain Lookup Failed

Additionally, callback integrations from Salesforce to customer domain names may fail due to DNS name resolution failures (UnknownHostException).

Løsning

    To resolve Salesforce email deliverability failures caused by DNS non-compliance, work with your DNS hosting vendor to ensure the recipient domain's infrastructure is fully compliant with current DNS standards. The following steps address the most common root causes.

    Steps to Resolve DNS Non-Compliance

    • Work with your DNS hosting vendor for full compliance to DNS standards and testing. This includes Mail servers, Web servers, Filtering services, Security appliances, and Load Balancers.
    • Ensure firewalls between the internet and DNS servers are up to date and capable of complying with the full range of DNS standards.
    • Ensure DNS Load Balancers are up to date and can handle EDNS0 cookies.
    • Ensure DNS server software is up to date and compliant with current DNS standards.
    • For information on current DNS standards, conformance tests, and related enforcement milestones, see https://dnsflagday.net/

    Note: Tests must be run with relevant, valid fully qualified domain names against DNS server IPs that are authoritative for the namespace.

    Knowledge-artikkelnummer

    000380393

     
    Laster
    Salesforce Help | Article