Error messages on sending and receiving emails

In the following, you will find an explanation for the most important error messages displayed by the mail system in case of delivery issues.

4xy Rate limit reached. Please try again later

Too many messages have been received in a short period of time. Please try again in a few hours and reduce the sending rate. If this does not help, you or your administrator can contact us here.

No “IP warming” is required when sending newsletters with trustedDialog.

4xy Reject due to policy violations

For administrative reasons, email delivery is temporarily not permitted. Please follow our email policy in order to ensure a trouble-free email communication.

4xy Administrative reject

Your e-mail was temporarily rejected due to a general system overload.

5xy Reject due to SPF policy. The originating IP of the message is not permitted by the domain owner

The email was rejected, because it was sent from a server that is not included in the domain owner's SPF record. This usually indicates that the sender address has been spoofed and that the email is spam/phishing.

Information for administrators: Should you offer an email forwarding service without rewriting the MAIL FROM, we would strongly advise you to implement SRS (Sender Rewriting Scheme), to avoid unwanted rejections.

Information for users: Should your forwarded emails not be delivered to your inbox, we would advise you to replace the mail forwarding with the Mail Collector service available in your account. This service will automatically retrieve emails from other mailboxes:

Should you have signed up to newsletters, we would advise you to use the email address you have with us for your subscriptions. This will avoid getting your subscriptions accidentally cancelled by the sender due to a failed email forwarding.

The trustedDialog email seal and brand logo of the sending company in the inbox indicates that the newsletter comes from a trustworthy sender.

5xy Syntax error in parameters or arguments

Due to an incorrect configuration, email reception has been refused. Please contact your administrator who should correct the server configuration based on our recommendations. Please contact your administrator who should correct the server configuration based on our recommendations and apply to us for the systems to be unblocked.

5xy Requested action not taken: mailbox unavailable

The specified recipient does not exist on our systems or the recipient has not used their inbox for an extended period of time and the inbox has been temporarily disabled due to inactivity. Please check the spelling of the email address.

5xy Bad DNS PTR resource record

Emails from your email server were rejected because the PTR Resource Record (PTR-RR) of your IP address does not follow our guidelines. Possible reasons for this can be:

5xy Reject due to policy restrictions (header based)

Your message will be rejected by our system if: any of the technical information included in the email doesn't meet the RFC 5321 and RFC 5322 standards, the email violates our guidelines or, it is not plausible, i.e.: when specifying the date. This is applicable to all emails with more than one of the following headers: BCC, CC, Date, From, Sender, Subject, To. In addition, the headers "Date, From, Sender, To" must be syntactically correct.

5xy Reject due to policy restrictions (domain based)

The email has been rejected due to our current security policy. This may occur if the sender domain is known as a spam domain. To check if a domain is listed, you may use a lookup tool such as the following: Spamhaus. If you are still experiencing problems, please request your system administrator to contact us.

5xy Reject due to policy restrictions (ip based)

The e-mail has been rejected because it violated our security policy: If a high percentage of e-mails are classified as spam by our filters, all messages coming from the sender's IP address will be temporarily rejected for a specific time frame.

In case the issue still persists, even if you cleaned up your system, you can contact us here.

5xy 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 inbox. Please use a different method to contact the person in question and inform them of the situation.

5xy IP address is block listed

To reduce spam email reception, 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 and/or email provider who should check if the IP address they use is on one of these RBL (Realtime Blackhole List) and who should then take the necessary steps to have the IP removed. In addition to this, we manage our own Black lists based on various criteria. If required, you or your administrator can contact us.

Thanks to the thorough sender authentication process, sending emails with trustedDialog reduces the probability of a legitimate sender being placed on an internal blocklist.

5xy Administrative reject

For administrative reasons delivery of emails to our systems is not permitted. Please contact the administrator of your system who should then contact us.

5xy Invalid DNS PTR resource record

The IP address of the email server you are using is not assigned to a domain name in the domain name service (DNS). Please contact your administrator to have the domain name added to the domain name service.

5xy Invalid DNS MX or A/AAAA resource record

The sender domain of the email server you are using has not been configured in agreement with the RFC guidelines in the domain name service (DNS). The following reasons may be responsible for this:

Please contact your administrator to correct the entry in the domain name service. A configuration check can be conducted under


  1. SPF (Sender Policy Framework) is a technology designed to make it more difficult to spoof sender addresses. It ascertains the IP addresses from which emails with a specific sender domain can be sent (or from which IP addresses mails may not be sent). To allow this to happen a TXT type (or SPF type if it exists) resource record is created in the DNS zone; it lists all the authorised IP addresses used as sending addresses in the domain. For more information on setting up an SPF record, see the website.
  2. When an email is redirected, a receiving system that validates email reception against an SPF entry is unable to validate the sender's identity. Forwarding servers should use SRS to encapsulate the sending address in an envelope to prevent SPF validation returning incorrect results. For more information on SRS refer to the site.
  3. A Reverse DNS entry or FQDN (Fully Qualified Domain Name or PTR-RR) is the unique name of an internet host. The FQDN can be used to discover the host's IP address. The Reverse DNS entry should be used as the HELO when sending emails.
  4. Short for Internet Protocol Address. An IP address comprises a numeric code of four numbers between 0 and 255 (e.g. ). More recent IP addresses (IPv6) are far longer and include numbers and the letters a-f separated by colons (e.g. 2001:8a2e:0370:0db8:85a3:7344:08d3:1319). This is the numeric address of a specific computer on the internet. Based on the IP address a computer on a network can be uniquely identified. To remove the need for users to remember numbers, the Domain Name System converts IP addresses into alphanumeric designators. Thus, the IP address resolves to Because IP addresses are a limited resource, private connections are typically assigned a dynamic IP address. If a connection with a dynamic address is interrupted, the next free address is assigned when the user dials up the network again. In contrast to this, a static IP address is mainly used for computers that offer services on the internet, and need to be available on the same IP address (e.g.
  5. Spam is undesirable email advertising. Professionals classify spam into Unsolicited Commercial Email (UCE). This is spam with a commercial background. Other mass mails are known as Unsolicited Bulk Email (UBE).
  6. A DNS based blackhole list is a real-time blocklist which contains IP addresses as well as faulty internet addresses. While processing emails, the information can be used in order to identify undesired messages and for example mark them as spam.
  7. An RBL list collects IP addresses. The list can be used to decide before establishing a connection if specific email senders are allowed to deliver to the receiving system, and to evaluate the spam probability with which emails are tagged. There are various types of lists of this kind. Some include IP addresses from which the owner is not prepared to receive and to which they are not prepared to send emails. Other lists include IP addresses which are known to be responsible for sending spam mail.
  8. RFC Indicates documents that describe the technical or organizational guidelines for the internet.
  9. The Mail Exchange Ressource Record of a domain is an entry in the domain name system, which specifies via what address the email server that is responsible for the domain can be reached.
  10. By means of the A-Record, a name gets allocated to an IPv4-address in the domain name system.
  11. Abbreviation for canonical name. It refers to the entry in the domain name system that specifies the primary name of a domain.