550: administrative reject
IONOS does not allow delivery from your system for administrative reasons. Only IONOS can say why, so the step is to contact it.
- IONOS
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550
- 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 sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 Administrative reject
What it means
An administrative reject means IONOS has decided, for reasons of its own, not to accept mail from your system. The help page gives no further detail and only one remedy: contact IONOS to have the problem checked. Since nothing in the bounce tells you the cause, it is worth making sure the usual requirements are met before you write, so the review is not held up by a second problem: a static IP with proper reverse DNS, a valid HELO name, no blocklist listings, and authenticated mail.
Common causes
- IONOS has blocked your system or domain by decision after a problem it observed.
- The block is a leftover from earlier abuse from your IP or domain.
How to fix it
- 01Check your IP and domain on public blocklists and your PTR, HELO, SPF and DKIM setup.
- 02Stop any unwanted outbound mail you find.
- 03Contact IONOS through its postmaster contact form (postmaster-contact.ionos.com) to have the block checked, quoting the full error.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 421Temporary reject under an exceptional blocklist.GMX refused the connection from your server for now under one of the blocklists it applies in exceptional situations. Your server will retry; GMX asks you to stop the misuse first, then contact it.
- 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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