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SMTP Error Messages for the 1&1 Mail Server

Here you can find an overview of error messages that our mail system issues if e-mails cannot be delivered to 1&1 mailboxes:

Error message Cause
421 Reject due to policy violations Due to a poor delivery rate (mail sent to too many e-mail addresses that do not exist), the IP address of your e-mail server is currently blocked for the delivery of e-mails.

Please correct the issue and try again later.
421 Rate limit reached. Please try again later Too many e-mails were sent in too short a time. Please try again in a couple of hours and reduce the dispatch rate.
450 Reject due to policy violations. This error may be caused by the following issues:

1. The delivery of e-mails has been temporarily delayed because a HELO/EHLO entry on the mail server is constantly changing. Generally, e-mail servers use a unique HELO entry for each IP address. Changing HELO entries in the SMTP dialog indicate that a system may have been infiltrated and manipulated to send spam by a virus. If our systems detect such an attempt, e-mails are temporarily rejected.

2. Since an e-mail was sent to too many mailboxes that do not exist, the IP address of your e-mail server is currently blocked from sending e-mails. Please correct the issue and try again later.
451 Requested action aborted: local error in processing The e-mail could not be delivered successfully because the service was temporarily unavailable. Please try again later.

Tip: For e-mails to be delivered successfully, it is important that the responsible DNS server always responds to the resolution of the DNS query quickly. If problems persist, you should therefore inform the sender domain administrator so that the administrator can ensure that the name is resolved quickly.
550 Syntax error in parameters or arguments E-mail reception has been denied due to an incorrect configuration. Please contact your administrator, who should correct the server configuration based on our recommendations.
550 Requested action not taken: mailbox unavailable The specified recipient does not exist in our system or the recipient has not used their mailbox for an extended period of time and it has been temporarily disabled due to inactivity. Please check the spelling of the email address.
550 Reject due to policy restrictions The e-mail has been rejected because it violates our security policy. Possible reasons include:

1. The sender domain that you use is known as a spam domain. To check if a domain is listed as a spam domain, you can use the Spamhaus service provider, for example.

2. The HELO/EHLO entry for the mail server does not match any fully qualified domain names (FQDN) and therefore has to be assigned appropriately by the mail system operator.

If the error continues to occur, please inform your administrator so that they can contact us.
550 Administrative reject The delivery of emails is not permitted for administrative reasons. Please contact the administrator of your system who should then contact us.
550 Invalid DNS MX or A/AAAA resource record The sender domain of the e-mail server that you are using is not configured to be RFC-compliant in the domain name service (DNS). This may be caused by the following issues:

1. No A record or MX record is configured for the sender domain in the DNS.

2. The MX record references a domain name that cannot be resolved.

3. The MX record references an IP address directly.

4. The MX server does not have a valid A record; instead, it has only a CNAME record.

Please contact your administrator so that they can correct the incorrect entry in the domain name service. You can perform a check of your configuration at
552 Requested mail action aborted: exceeded storage allocation, Quota exceeded We were unable to deliver your email because the potential recipient does not have sufficient free space in their mailbox. Please use a different method to contact the person in question and inform them of the situation.
554 Invalid DNS PTR resource record The IP address of the e-mail server that you are using is not allocated a domain name in the domain name service (DNS). Please contact your administrator to add the missing entry in the domain name service.
554 Bad DNS PTR resource record E-mails from your e-mail server were rejected because the PTR resource record (PTR-RR) for your IP address does not meet our guidelines. Possible reasons for this include:

1. The PTR-RR reveals that the IP address is assigned dynamically.

2. The PTR-RR is a generic default entry from your provider. Please assign an individual, complete domain name (fully qualified domain name, FQDN) to your e-mail server and enter a valid PTR-RR accordingly.

If you are not the mail server operator, please contact your responsible administrator or the customer service department of your provider.
554 IP address is blacklisted To reduce the amount of e-mail spam received, we use popular DNSBL lists (DNS-based Blackhole List). These lists contain dynamic IP addresses and IP addresses currently known to be spam senders. Please contact your system administrator or e-mail provider so that they can check whether your IP address is on one of these RBL lists and take steps to remove it. In addition to this, we manage our own RBL lists based on various criteria. If required, you or your administrator can contact us.
554 Rejected due to policy restrictions The e-mail has been rejected because it violates our security policy regarding the ratio of e-mails classified as spam in relation to the total number of e-mails sent by the mail server.

If the error continues to occur over an extended period of time, please have your administrator(s) contact us.