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Error code wiki · 57 codes

GMX, WEB.DE and mail.com SMTP error codes

GMX, WEB.DE and mail.com run on one mail platform with one postmaster team, so mail to their addresses meets the same filters and the same case-numbered error messages.

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Permanent failures (5xx)

33 codes

The receiving server refused the message for good. Your server will not try again, and the message comes back to you as a bounce.

  1. 550Permanent reject under an exceptional blocklist.GMX permanently refused mail from your system because it is on one of the blocklists GMX uses in exceptional situations. The message comes back and is not retried.Permanent
  2. 550HELO 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.Permanent
  3. 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.Permanent
  4. 550Envelope domain on a GMX blocklist.GMX refused your mail because the domain in your envelope sender (MAIL FROM) is on one of its own blocklists.Permanent
  5. 550Sender domain on a Spamhaus blocklist.GMX refused your mail because your envelope or From domain is listed on a Spamhaus blocklist. GMX makes no exceptions; the listing must be removed at Spamhaus.Permanent
  6. 550Sender domain has no valid MX or A record.GMX refused the mail because your sender domain is not set up in DNS as the RFCs require: it needs an MX record whose host has a valid A record.Permanent
  7. 550Sender domain publishes a null MX.GMX refused the mail because your sender domain publishes a null MX record, which says the domain accepts no email. GMX only takes mail from domains that can receive replies.Permanent
  8. 550Mailbox does not exist or is disabled.The GMX, WEB.DE or mail.com address you wrote to does not exist, was disabled after a long period without use, or was blocked by the provider.Permanent
  9. 550Recipient domain has no valid MX or A record.The recipient's domain is not set up in DNS as the RFCs require, with an MX record whose host has a valid A record, so GMX refused the mail.Permanent
  10. 550Recipient domain does not exist.The domain in the recipient address did not exist in DNS when GMX tried to deliver (NXDOMAIN), so the message could not be delivered.Permanent
  11. 552Recipient mailbox is full.The recipient's GMX mailbox has no room left, either in storage or in the number of emails it may hold, so the message was refused.Permanent
  12. 552Message too large.The message is larger than the recipient mailbox or the GMX server accepts, so it was refused. Make it smaller and send it again.Permanent
  13. 554Rejected for breaking GMX guidelines.GMX refused the message permanently because the connection broke its guidelines. GMX points to its requirements page and asks for the full error message if the problem continues.Permanent
  14. 554IP address on the GMX blocklist.Your sending IP is on a blocklist that GMX manages itself, so its servers refuse the connection. GMX keeps a strict no tolerance policy toward spam.Permanent
  15. 554IP address on a Spamhaus blocklist.GMX refused the connection because your sending IP is listed on a Spamhaus blocklist. GMX makes no exceptions; the listing has to be removed at Spamhaus.Permanent
  16. 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.Permanent
  17. 554No reverse DNS for your IP.GMX refused the connection because the IP address of your mail server has no PTR record, so it is not tied to any domain name in DNS.Permanent
  18. 554Forward-confirmed reverse DNS failed.GMX refused the connection because the name in your IP address PTR record does not resolve back to that same IP, so the FCrDNS check failed.Permanent
  19. 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.Permanent
  20. 554Rejected under the sender domain's DMARC policy.The message failed SPF and DKIM as DMARC requires, and the From domain publishes p=reject, so GMX rejected it as the domain owner asked.Permanent
  21. 554HELO name changes or fails reverse lookup (554).GMX refused the mail with a 554 because your server uses alternating HELO names, or its HELO name failed the reverse lookup.Permanent
  22. 554Date header is far from the real time.GMX refused the message because the date and time in its Date header are implausible, too far from the actual time. Correct the clock on the server or client.Permanent
  23. 554A header field appears more than once.GMX refused the message because a header that RFC 5322 allows only once, such as From, Date, Subject or Message-Id, appears more than once.Permanent
  24. 554Required Date or From header is missing.GMX refused the message because it has no Date header or no From header, both of which RFC 5322 requires in every message.Permanent
  25. 554A header field has invalid syntax.GMX refused the message because a header, such as Date, From, Sender, Subject or To, is not written the way RFC 5322 and RFC 2047 require.Permanent
  26. 554Too many copies of one header field.GMX refused the message because one header field, such as DKIM-Signature, List-Unsubscribe or Resent-From, appears more often than GMX accepts.Permanent
  27. 554DKIM-Signature header has invalid syntax.GMX refused the message because its DKIM-Signature header does not follow the syntax that RFC 6376 defines for it, so the header itself is malformed.Permanent
  28. 554More than one address in the From header.GMX refused the message because its From header lists more than one email address. GMX accepts only one address in From.Permanent
  29. 554Bare LF or CR in the message.GMX refused the message because it contains a line feed or carriage return on its own. RFC 5322 requires them only as a CRLF pair.Permanent
  30. 554Mail loop detected.GMX refused the message because it is going round in a loop, usually between forwarding rules that send it back and forth.Permanent
  31. 554Link to a URL on a GMX blocklist.GMX refused the message because it contains a URL that is on one of the GMX blocklists. Remove the link or have the listing reviewed.Permanent
  32. 554Link to a domain on the Spamhaus DBL.GMX refused the message because it links to a domain listed on the Spamhaus Domain Block List (DBL). The listing has to be resolved at Spamhaus.Permanent
  33. 556Recipient domain publishes a null MX.The domain you are writing to publishes a null MX record, which declares that it accepts no email, so the message cannot be delivered.Permanent

Temporary failures (4xx)

24 codes

The receiving server cannot take the message now. Your server keeps it and retries, and only bounces it if the retries run out.

  1. 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.Temporary
  2. 421Too 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.Temporary
  3. 421Too many mails to addresses that do not exist.GMX is turning your server away for a while because it sent too much mail to GMX addresses that do not exist. Clean the list before sending again.Temporary
  4. 421Reverse DNS lookup failed for now.GMX could not look up your IP address reverse DNS because of a temporary DNS error, so it deferred the connection. Your server's retry usually succeeds.Temporary
  5. 421Connection ended by a temporary error.A temporary error occurred in the connection between your server and GMX, so GMX closed it. Another delivery attempt later should go through.Temporary
  6. 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.Temporary
  7. 421Too many connections from your IP.Your server opened more simultaneous connections to a GMX mail server than one IP may hold. Wait for an open connection to close, then connect again.Temporary
  8. 450Deferred for mail to unknown addresses.GMX deferred your mail with a 450 because your server has been sending to too many GMX addresses that do not exist.Temporary
  9. 450Too many messages in a short time (450).GMX blocked your system for a while with a 450 because it received too many messages from it in a short period. The limit can be raised on request.Temporary
  10. 450Recipient is receiving too fast.GMX deferred mail to one recipient because it was being sent too often or with too many parallel attempts. It will be accepted on a later retry.Temporary
  11. 450Mailbox temporarily unavailable.The GMX mailbox is unavailable at the moment, so the message was deferred. Your server will retry several times; if it lasts, reach the recipient another way.Temporary
  12. 450E-Mail Made in Germany requirements not met.GMX rejected the connection because it did not meet the requirements of E-Mail Made in Germany (EMiG), usually because of missing or inadequate encryption.Temporary
  13. 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.Temporary
  14. 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.Temporary
  15. 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.Temporary
  16. 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.Temporary
  17. 451Low DKIM domain reputation.GMX deferred your mail because unusually high traffic arrived from a DKIM signing domain with a low reputation at GMX.Temporary
  18. 451Poor reputation of your network area.GMX deferred your mail because unexpected volume arrived from a network area with a negative reputation. An automatic check of your DKIM domain follows.Temporary
  19. 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.Temporary
  20. 451Suspected replay attack.GMX deferred your mail because inconsistent details in the delivery, combined with high traffic, suggested a replay attack. Report it if you think this is a mistake.Temporary
  21. 451Envelope sender breaks GMX guidelines.GMX deferred the message because the sender information in the envelope (MAIL FROM) breaks its guidelines. Check that the MAIL FROM address is complete and correct.Temporary
  22. 451DKIM domain suspended for spam.GMX found a massive amount of spam signed with your DKIM domain and sent through your mail system, and has suspended acceptance of mail from them.Temporary
  23. 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.Temporary
  24. 452Too many recipients in one message.Your server named more recipients in one transaction than GMX accepts, currently 20 per message, so the rest were deferred. Split the recipients into several transactions.Temporary

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