If the transmission of an email to GMX or the connection of your mail server to our GMX mail servers fails, our servers always issue a detailed error message during the SMTP dialog, with the structure described below.
The Non-Delivery Report (NDR), which is sent to the sender by email, is created by the sending mail server - not by GMX.
The error message issued by GMX is multi-line. The last line of the multi-line error message is decisive for a well-founded analysis, as it contains the relevant detailed information.
In addition, the error message contains a specific URL that links to a separate postmaster page for the error, which shows explanations and solutions, as well as a way to contact us if the problem needs to be solved from our side.
1. Permanent errors (5xx codes)
These errors indicate a permanent problem. The email should not be delivered again.
2. Temporary errors (4xx codes)
These errors are temporary. Subsequent delivery may be successful. In such cases, we recommend automated delivery attempts (retries) by the sending mail server.
Error messages issued by our mail servers consist of:
550, 421, but we do not use any additional Enhanced Status Codes, e.g. 5.1.1).Here is an example where the connection was rejected because the IP address of the delivering mail server was on a block list:
554-gmx.net (mxgmx104) Nemesis ESMTP Service not available 554-No SMTP service 554-IP address is block listed. 554 For explanation visit https://postmaster.gmx.net/en/case?c=r0201&i=ip&v=198.51.100.42&r=1MNcgj-1ue23t3pyV-00S2YR
If problems occur when sending emails to our customers' email addresses or when establishing a connection to our mail servers, senders receive so-called non-delivery reports (NDRs) or bounces in the form of an email via their own mail server. This means that the email is not sent by our systems, but by the mail system that wanted to deliver the actual email to us.
This email (the NDR) usually contains the error message with which our mail system rejected the delivery in the dialog with the delivering mail system (i.e. during the SMTP dialog).
Not all mail systems include the complete error message in the NDR, so that relevant information may be missing that would be helpful or even absolutely necessary in case of an analysis of the problem by our Postmaster Team.
It can even happen that delivering mail systems try to interpret the error message from our mail system and then do not include our error message 1:1 in the NDR. Such information is worthless for problem analysis. In these cases, however, the person responsible for the mail system should be able to find the original error message from our mail system in their own log files.
For an analysis on our side, the entire last line of our error message is relevant.
You can identify the related error messages in your logs by searching for the URL pattern https://postmaster.(gmx|web|mail) tun.