550 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain
The recipient's domain does not exist in DNS
Seen in Exchange, Microsoft 365, Postfix (Host or domain name not found)
The sending server could not find the recipient's domain in DNS (no MX, A or AAAA record), so it has nowhere to deliver the message.
Common causes
- A typo in the domain, such as gmial.com or example.con.
- The domain has expired or its DNS zone was deleted.
- The domain exists but has no MX record and no A or AAAA record to fall back on.
How to fix it
- Check the spelling of the domain part of the address.
- Look up the MX record; if there is none, the recipient must fix their DNS.
- If every domain fails, check the sending server's own DNS resolver.
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Related errors
- 550 5.1.1 User unknown · The recipient address doesn't exist
- 550 5.1.10 RESOLVER.ADR.RecipientNotFound · Microsoft 365 could not find the recipient
- 554 5.7.1 <user@example.com>: Relay access denied · Postfix refused to relay to that recipient
- 450 4.1.8 <user@example.com>: Sender address rejected: Domain not found · The sender's domain does not resolve in DNS
- 550 5.7.26 Unauthenticated email is not accepted · Gmail rejected mail that failed DMARC
- 550 5.7.25 The IP address sending this message does not have a PTR record · The sending IP has no reverse DNS
- 550 5.7.1 Relaying denied / Message rejected · The receiving server refused the message on policy grounds
- 554 5.7.1 Service unavailable; Client host blocked using a blocklist · The sending IP is on a blocklist
- 421 4.7.0 Try again later · Temporarily deferred by the receiving server
- 550 5.7.515 Access denied, sending domain does not meet the required authentication level · Outlook.com rejected unauthenticated bulk mail
- 550 5.7.23 SPF validation failed · The message failed the SPF check
- 550 5.4.1 Recipient address rejected: Access denied · Microsoft 365 rejected an unknown recipient at the edge