421: too much of your mail is spam
GMX is refusing mail from your server for a while because too large a share of its recent mail was classed as spam by the GMX filters.
- GMX, WEB.DE
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421
- 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
421 Reject due to policy restrictions.
What it means
Case r1201 is a temporary block based on proportion. The GMX filtering system judged too many of the emails from your server to be spam, measured against everything the server sent, and GMX stopped accepting its mail for a period. Because the reply is a 421, your server keeps the messages and tries again. The block lifts on its own, and it can return while the share of spam stays high. GMX asks you to stop spam from leaving your system and to make sure the server cannot be used without authorisation.
Common causes
- A large share of the mail from your server was spam or looked like it.
- A compromised account or open relay was sending spam alongside your normal mail.
- A campaign went to recipients who did not ask for it, and the filters scored it as spam.
How to fix it
- 01Stop or slow down sending to GMX addresses until you know where the spam came from.
- 02Check the server for unauthorised access: open relay settings, weak passwords, exposed scripts.
- 03Send bulk mail only to recipients who gave consent, ideally through double opt-in, as GMX asks of bulk senders.
- 04Let the server retry once the source is closed.
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 r1201: 421 Reject due to policy restrictionspostmaster.gmx.net
Related codes
- 451Message closely resembles spam.GMX deferred this message because it looks very much like known spam. Check your system for abuse, and sign with an aligned DKIM domain to improve its standing.
- 554System and domain suspended for spam.GMX permanently refused your mail after a massive amount of spam reached its customers through your mail system and domain, and suspended their privileges.
- 421Service not available.The receiving server is closing the connection and will not take mail right now. The reply is temporary, so the sending server keeps the message and tries again later.
421 at other providers
- 421 [RP-001]Outlook.com rate limit for the sending IP.Outlook.com is limiting how fast your IP can send to it because of the IP or domain's reputation; it is temporary and your server should retry.
- 421 [RP-002]Outlook.com rate limit on this connection.Your IP has sent more over a single connection than Outlook.com allows, a limit Microsoft ties to IP and domain reputation.
- 421 [RP-003]Outlook.com connection limit.Your IP has opened more connections to Outlook.com than it is allowed, a limit Microsoft links to IP and domain reputation.
- 421Temporary error or deferral.Yahoo or AOL refused your message for now with a 421, one of its two temporary error codes. Your server should keep it and retry; repeated deferrals point to reputation or complaints.
- 421Try again later.Xfinity turned the message away for now with a generic 421. Treat it as temporary and let your server retry: Xfinity uses it for several reasons it does not spell out.
- 421Reverse DNS lookup failed.Xfinity could not complete a reverse DNS lookup for your sending IP. It treats this as temporary, so your server should retry, but a broken DNS setup keeps it failing.
Further reading
All 57 GMX, WEB.DE codesEvery code in the wikiPaste your own bounce