451: local error in processing
IONOS could not accept the message because the service was temporarily unavailable. IONOS points to slow DNS answers from the sending side as the thing to check.
- IONOS
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 451
- Provider
- IONOS (1&1)
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
451 Requested action aborted: local error in processing
What it means
This 451 is a temporary failure: the message could not be delivered because the service was briefly unavailable, and your server will try again. The IONOS help page ties it to DNS: its only advice is to make sure the DNS service of your system answers queries quickly, which points to a lookup on the sending side that took too long. A single 451 can be left to the retry; repeated ones point to the name servers behind your domain or your reverse DNS.
Common causes
- The name servers for your domain or your IP reverse zone answer slowly.
- A short outage on the IONOS side.
How to fix it
- 01Let your server retry the message.
- 02If it repeats, time DNS queries for your domain and your PTR record from outside your network.
- 03Fix or replace slow name servers, or ask your DNS provider to.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 451Temporary DNS error during the MX lookup.GMX could not complete the MX lookup for the sender or recipient domain because of a temporary DNS error, so it deferred the message.
- 451Local error in processing.The receiving server hit a problem on its own side while handling the message and stopped. The reply is temporary, so the sending server will try again.
451 at other providers
- 451Sender domain could not be resolved.Yahoo could not confirm that the domain in your envelope sender or From address exists. As a 451 it is temporary; Yahoo can also return the same problem as a permanent 554.
- 451Temporary reject for misuse or guideline violations.GMX deferred your mail with a 451 because of an exceptional blocklist or a breach of its sending guidelines. The message is retried, but the cause has to be removed first.
- 451Transaction limit per session reached.Your server sent more messages over one SMTP session than GMX allows, currently 100, so GMX deferred the next one. Close the session and open a new one.
- 451Far more mail than expected.GMX received far more mail than it expected from your system, your DKIM domain or your network, and deferred the rest for now. A higher limit can be requested.
- 451Missing or unaligned DKIM under high traffic.GMX deferred your mail because it arrived in unusual volume without a DKIM signature that matches the From domain. Sign with an aligned DKIM domain to clear it.
- 451Low DKIM domain reputation.GMX deferred your mail because unusually high traffic arrived from a DKIM signing domain with a low reputation at GMX.
Further reading
All 17 IONOS codesEvery code in the wikiPaste your own bounce