550: recipient domain has no valid MX or A record
The recipient's domain is not set up in DNS as the RFCs require, with an MX record whose host has a valid A record, so GMX refused the mail.
- GMX, WEB.DE
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550
- Provider
- GMX, WEB.DE and mail.com
- 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
550 invalid DNS MX or A/AAAA resource record
What it means
Case r1404 mirrors case r1401 for the recipient side: the domain you are writing to is not configured in line with the RFCs. GMX expects an MX record that points to a host with its own valid A record (RFC 5321 section 5.1, RFC 2181 section 10.3). A mistyped domain can be the whole cause. Otherwise the records have to be corrected by whoever runs the domain, so GMX directs questions to the recipient domain administrator. It also notes that it cannot answer an inquiry from that same domain while the error remains.
Common causes
- The domain in the address is misspelled.
- The recipient domain has no MX record, or its MX host does not resolve.
- The MX record points to an alias or an IP address instead of a host name with an A record.
How to fix it
- 01Check the spelling of the recipient domain.
- 02Look up its MX records and the A record of each MX host.
- 03Tell the recipient or the domain's administrator what is missing, using another channel.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- GMX Postmaster case r1404: 550 invalid DNS MX or A/AAAA resource recordpostmaster.gmx.net
Related codes
- 550Sender domain has no valid MX or A record.GMX refused the mail because your sender domain is not set up in DNS as the RFCs require: it needs an MX record whose host has a valid A record.
- 550Recipient domain does not exist.The domain in the recipient address did not exist in DNS when GMX tried to deliver (NXDOMAIN), so the message could not be delivered.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
550 at other providers
- 550 [SC-001]Outlook.com policy block for content or reputation.Outlook.com rejected the mail for policy reasons tied to spam-like content or to the reputation of the sending IP or domain.
- 550 [SC-002]Outlook.com block for namespace mining.Outlook.com blocked the sending IP because it behaved like a namespace miner, checking whether addresses exist without sending mail.
- 550 [SC-003]Outlook.com block for an open proxy or relay.Outlook.com rejected the mail because the sending IP appears to be an open proxy or open relay.
- 550 [SC-004]Outlook.com block after complaints.Outlook.com placed a block on the sending IP because it received complaints about mail coming from it.
- 550 [DY-001]Outlook.com refuses dynamic IP addresses.Outlook.com rejected the mail because the sending IP is dynamic address space, which it generally does not accept mail from.
- 550 [DY-002]Outlook.com block for a likely compromised sender.Outlook.com rejected the mail because the sending server or computer appears to be compromised or infected.
Further reading
All 57 GMX, WEB.DE codesEvery code in the wikiPaste your own bounce