550: HELO name not accepted
GMX refused your mail because the HELO name your server announces is not a resolvable host name, or is on the GMX internal HELO blocklist.
- 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 sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 Reject due to policy restrictions
What it means
Every SMTP session opens with HELO or EHLO, where the sending server names itself (RFC 5321). GMX expects that name to be a fully qualified domain name that resolves to an IP address, so it can validate the server. Case r0801 gives two reasons for refusing it. Either the name does not resolve, which includes generic names such as localhost.localdomain, or it is on an internal GMX list of HELO names blocked after security problems or abuse. The fix is a proper host name. If the name is already valid and the error continues, GMX asks you to contact it and state the HELO you use.
Common causes
- The server announces localhost, a bare host name or a name that does not exist in DNS.
- The HELO name was copied from a template or default configuration.
- The name you use is on the GMX internal HELO blocklist after abuse elsewhere.
How to fix it
- 01Set the HELO/EHLO name to a fully qualified host name in your domain, such as mail.yourdomain.tld.
- 02Make that name resolve to the sending IP, and ideally match the PTR record.
- 03Restart the mail service and confirm the new name in a test session.
- 04If the name is valid and still refused, contact GMX through the case page form and state the HELO you use.
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 r0801: 550 Reject due to policy restrictionspostmaster.gmx.net
Related codes
- 550HELO name changes or fails reverse lookup.GMX refused the mail because your server announces different HELO names from one connection to the next, or the reverse lookup of its HELO name failed.
- 554Reverse DNS does not meet GMX requirements.GMX refused the connection because the reverse DNS (PTR) record of your IP looks generic or dynamic. GMX expects a fixed IP with its own mail host name.
- 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.
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