SMTP Error Messages of the 1&1 IONOS Mail Servers

Here you will find an overview of the error messages that our mail system issues when emails cannot be delivered to 1&1 IONOS mailboxes:

421 Reject due to policy violations:

Due to a poor delivery rate (sending to too many non-existent email addresses), the IP address of your email server is currently blocked for the delivery of emails. The main causes for a poor delivery rate are either outdated address lists for newsletters and other mass mailings or compromised mailboxes that are misused for sending spam. Please correct the cause and try again at a later time.

421 Rate limit reached. Please try again later:

Too many emails were delivered in too short a time. Please try again in a few hours and then reduce the shipping rate.

450 Reject due to policy violations:

This error may be caused by the following:

  • The delivery of emails was temporarily delayed due to a constantly changing HELO/EHLO entry of the shipping server. Usually, email servers use a unique HELO entry per IP address. Changing HELO entries in the SMTP dialog indicate a potentially infected system that is being abused by a virus to send spam. If our systems detect such an attempt, emails are temporarily rejected.
  • Your server's IP address is currently blocked for email delivery because too many non-existent email addresses have been written to (poor delivery rate). The main causes are usually outdated address lists for newsletters and other mass mailings or compromised mailboxes that are misused to send spam.

Please correct the cause and try again at a later time.

451 Requested action aborted: local error in processing:

The email could not be delivered successfully because the service was temporarily unavailable. Please try again later.

Please note: For emails to be delivered successfully, it is important, among other things, that the resolution of the DNS query is always answered quickly by the responsible DNS service. If problems persist, you should therefore inform the administrator of the sender domain so that he can ensure a fast name resolution.

550 Syntax error in parameters or arguments:

Due to an incorrect configuration, the receipt of emails is rejected. Please contact your administrator so that they can configure the server correctly based on our recommendations.

550 Requested action not taken: mailbox unavailable:

The specified recipient does not exist in our system or has not used his or her mailbox for too long and has been temporarily deactivated due to inactivity. Please check the spelling of this email address.

550 Reject due to policy restrictions:

The email was rejected because it violates our policies. Possible reasons could be:

  • The sender domain you are using is known as a spam domain. A check is possible, for example, via the provider Spamhaus.
  • The HELO/EHLO entry of the shipping server does not correspond to a fully qualified domain name (FQDN) and must therefore be assigned accordingly by the mail system operator.

If the error persists, please contact your administrator so that they can contact us.

550 Administrative reject:

For administrative reasons it is not allowed to deliver emails. Please contact the administrator of your system so that he can contact us.

550 Invalid DNS MX or A/AAAA resource record:

The sender domain of the email server you are using is not configured RFC-compliant in the domain name service (DNS). This may be due to the following causes:

  • Neither an A nor an MX record is configured in the DNS for the sender domain.
  • The MX record refers to a domain name that cannot be resolved.
  • The MX record refers directly to an IP address.
  • The MX server does not have a valid A-record but only a CNAME record.

Please contact your administrator to correct the incorrect entry in the domain name service. You can check your configuration at http://www.intodns.com/

552 Requested mail action aborted: exceeded storage allocation, Quota exceeded:

Your email could not be delivered because the potential recipient has no free space in his mailbox. Please contact the person by other means and point this out.

554 Invalid DNS PTR resource record:

The IP address of the email server you use is not assigned a domain name in the domain name service (DNS). Please contact your administrator to make the missing entry in the domain name service.

554 Bad DNS PTR resource record:

Emails from your email server have been rejected because the PTR Resource Record (PTR-RR) of your IP address does not comply with our policies. Possible reasons for this could be:

  • The PTR-RR indicates that the IP address is dynamically assigned.
  • The PTR-RR is your provider's default generic entry. Please assign your email server its own complete domain name (Fully Qualified Domain Name - FQDN) and enter a valid PTR-RR.

If you are not the operator of the mail server yourself, please contact your responsible administrator or the customer service of your provider.

554 IP address is black listed:

In order to reduce the receipt of email spam, we use common DNSBL lists (DNS-based Blackhole List). These lists contain dynamic IP addresses on the one hand and IP addresses from which spam is currently sent on the other. Please contact your system administrator or email provider to check if your IP address is on an appropriate RBL list and take steps to unsubscribe. In addition, we maintain our own RBL lists based on various criteria. If necessary, you or your administrator can contact us.

554 Reject due to policy restrictions:

The email was rejected because it violates our policies. The sending server mainly transmits spam messages. If the error occurs over a longer period of time, please contact your administrator so that they can contact us.