550 5.4.310 DNS domain does not exist
A Microsoft 365 user tried to send to a domain and Exchange Online could not find it in DNS: no MX record, no A record, nothing. This is a bounce for mail leaving Microsoft, and it means the recipient domain is misspelled, expired or has never had mail set up.
What the server replies
550 5.4.310 DNS domain example.invalid does not exist [Message=InfoDomainNonexistent] [LastAttemptedServerName=example.invalid] [LastAttemptedIP=] [AM0PR06MB1234.eurprd06.prod.outlook.com]
- Sent by
- Microsoft 365
- Type
- PermanentRetry fails
- About
- Recipient problems
- Enhanced code
- 5.4.310
Who sends it
Exchange Online transport when it tries to route an outbound message and the DNS lookup for the recipient domain returns NXDOMAIN. Sender is a Microsoft 365 mailbox; the NDR comes from the tenant's own servers.
Why it happens
- A typo in the recipient domain (gmial.com, outlok.com).
- The recipient's domain registration lapsed and its DNS zone disappeared.
- The domain exists but has no MX and no A record, so there is nowhere to deliver.
- The domain is brand new and its nameservers have not propagated yet.
How to fix it
Check the spelling
Most of these are typos. Compare the domain against a known-good message from the recipient.
Look the domain up
Run the domain through an email DNS checker. If there are no MX and no A records, the recipient has to fix their DNS; nothing on the sending side will deliver it.
Retry once for a new domain
If the domain was registered today, DNS can take an hour or two to appear at Microsoft's resolvers. Resend later.
Check it yourself
These free tools show the records and connections behind this code for your own domain or server.
Related codes
- 550 5.1.2 Host unknown / bad destination system addressThe domain part of the recipient address is the problem: it does not resolve, so no server can be found to deliver to.
- 553 5.1.8 Sender address rejected: Domain not foundThe receiving server looked up the domain in your envelope sender address and found nothing, so it refuses to accept mail it could never bounce back to you.
- 550 5.4.1 Recipient address rejected: Access deniedExchange Online looked the recipient up in the tenant's directory and did not find it, so it refused the address at RCPT TO.
Sources
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Other free tools
All tools- Email DNS checkerCheck MX, SPF, DKIM, DMARC and reverse DNS for any domain and get the exact records to add or fix.
- DMARC checkerLook up a domain's DMARC record, read every tag in plain words and see what to tighten next.
- DMARC record generatorBuild a valid DMARC record from a few choices and copy the host and value into your DNS.
- DMARC report analyzerDrop in a DMARC aggregate report and see who is sending as your domain and whether they pass.
- SMTP connection testerConnect to any SMTP server, check TLS and the login step, and see each stage with its timing.
- Email header analyzerPaste raw headers to see every hop, where the delay was, and whether SPF, DKIM and DMARC passed.
- Email address validatorCheck whether an address is well formed, whether its domain accepts mail, and whether it is disposable or a role account.