451: far 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.
- GMX, WEB.DE
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 451
- Provider
- GMX, WEB.DE and mail.com
- 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
What it means
GMX keeps an expectation of how much mail each sender normally delivers, and these cases mean the current volume went well past it. Case r2200 measures your email system or domain, r2201 the DKIM signing domain, and r2202 and r2203 the network area your server sits in. Because the behaviour is unusual, GMX temporarily refuses further mail with a 451. If you are refused again after the measure ends, GMX asks you to request a higher delivery limit through the form on the case page, quoting the full error together with the DKIM domain, IP addresses or AS number it asks for.
Common causes
- A large campaign or a sudden jump in volume compared with your usual traffic.
- Another sender in the same network area or sharing your DKIM domain sent a surge of mail.
- A compromised account sent a large volume under your domain.
How to fix it
- 01Spread large sends over time and raise volume to GMX gradually.
- 02Check that the surge was intended and not caused by misuse.
- 03Let the deferred mail retry after the measure ends.
- 04If you are refused again, ask for a higher limit through the case page form with the full error, your DKIM domain and your IPs or AS number.
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 r2200: 451 Reject due to policy restrictionspostmaster.gmx.net
- GMX Postmaster case r2201: 451 Reject due to policy restrictionspostmaster.gmx.net
- GMX Postmaster case r2202: 451 Reject due to policy restrictionspostmaster.gmx.net
- GMX Postmaster case r2203: 451 Reject due to policy restrictionspostmaster.gmx.net
Related codes
- 421Too many messages in a short time.GMX received too many messages from your system in a short period and blocked it for a while. GMX can raise the limit on request.
- 451Low DKIM domain reputation.GMX deferred your mail because unusually high traffic arrived from a DKIM signing domain with a low reputation at GMX.
- 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.
- 451Local 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.
- 451Greylisting or a reputation check delayed the message.Mimecast is holding off a first contact from your server through greylisting, or because your IP’s reputation is poor. A well-behaved server retries and usually gets through.
- 451Mimecast server at full load.The Mimecast server your message reached was at maximum load and asked your server to try again later. Nothing is wrong with your mail.
- 451Mimecast does not recognise either domain.Mimecast saw a message where neither the sender’s nor the recipient’s domain belongs to its customer, so it refused to pass it on, as relaying for outsiders is not allowed.
- 451Sending IP temporarily blocked for exceeding a limit.Your sending IP went over a limit Mimecast applies, so it is refused for now. Mail is accepted again once your traffic falls back under the limit.
Further reading
All 57 GMX, WEB.DE codesEvery code in the wikiPaste your own bounce