556: recipient domain publishes a null MX
The domain you are writing to has a No Service MX record (null MX), which means it can neither receive nor send email, so the message cannot be delivered.
- IONOS
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 556
- Provider
- IONOS (1&1)
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
556 Recipient address has null MX
What it means
A null MX (RFC 7505) is a domain declaring that it takes no mail. This 556 means the recipient domain has one, and IONOS describes such a domain as one that can neither receive nor send email. Retrying will not help. The IONOS advice is to contact the administrator of the receiving domain to have the entry checked, since only they can replace it with a real MX record. Check first that you have the right domain for the person you are writing to.
Common causes
- The recipient domain was set up as a no-mail domain.
- A parked or web-only domain template added the null MX.
- The address uses the wrong domain for the recipient.
How to fix it
- 01Check that the recipient domain is correct.
- 02Ask the recipient, by other means, for an address on a domain that receives mail.
- 03If you run the domain, replace the null MX with a real MX record.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 556Recipient domain publishes a null MX.The domain you are writing to publishes a null MX record, which declares that it accepts no email, so the message cannot be delivered.
- 550Sender domain publishes a null MX.Your sender domain publishes a No Service MX record (null MX), which says it accepts no mail, and IONOS rejects mail from such domains.
Further reading
All 17 IONOS codesEvery code in the wikiPaste your own bounce