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550 5.4.310: Microsoft says DNS domain does not exist

550 5.4.310DNS domain does not existPermanent: retrying will not helpFrom Microsoft 365 and Outlook.com

Typical wording
550 5.4.310 DNS domain example.com does not exist

What it means

When Exchange Online routes a message to an external domain it looks up the domain’s MX records. A 5.4.310 means that lookup came back as NXDOMAIN: the domain name itself does not exist in DNS. The NDR usually reads like the example, often followed by bracketed details naming the lookup result.

This is stronger than a missing MX. A domain with no MX but with an A record can still receive mail; a domain that returns NXDOMAIN has no records of any kind. That is why it is permanent and not retried, unlike 5.4.312 where the DNS query itself failed and may work later.

Likely causes

  • A typo in the domain part of the address, such as exmaple.com.
  • The recipient’s domain registration expired and the registry removed its delegation.
  • The domain’s nameservers were changed to hosts that do not serve the zone.
  • A mail contact in your tenant holds an outdated address at a domain that no longer exists.

How to fix it

  1. Check the domain spelling first.
  2. Look up the domain’s registration to see whether it expired or is in a redemption period.
  3. Recipient: renew the domain or fix the NS delegation at the registrar, then confirm the zone answers.
  4. Sender admin: update or delete stale contacts and distribution list members that point to the dead domain.

Checks that apply

  • Whois Lookup Shows whether the domain is registered, when it expires, and which nameservers it is delegated to.
  • DNS Server Audit Audits the delegated nameservers and shows whether they answer for the zone at all.
  • MX Lookup Confirms whether the domain now returns MX records after a fix.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Can the problem be on Microsoft’s side?
Very rarely. If public resolvers also return NXDOMAIN for the domain, the problem is the domain itself.
How quickly does it work after renewal?
Once the registry restores the delegation, usually within hours, though resolvers may cache the negative answer for the SOA minimum time.

Microsoft 365 delist portal Outlook.com SNDS

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