Delivery Status Notification (DSN) and Non-Delivery Notification (NDN) Messages
All too frequently, e-mail users are receiving "non-delivery reports" from servers even though no e-mail was sent to the server in the first place. In most cases, the addressee is completely unknown. These reports are not only confusing, but they also flood users' mailboxes with unwanted messages.
The format of delivery status notification (DSN) messages, including non-delivery reports, is defined in the relevant requests for comment (RfC), so every correctly implemented e-mail server (MTA) complies with this format. The advantage of this is that iQ.Suite can recognise such messages and, if necessary, filter them or move them to quarantine. One way of recognising these messages is by examining the "Form". The following mail formula rule identifies NDRs by checking the "Form" field for NDR-specific entries:
_formValue := form;
_isNdr := (@Contains(_formValue; "NonDelivery Report") | @Contains(_formValue; "Delivery Report"));
@If(@isError(_isNdr); @false; _isNdr)
You can move NDRs to quarantine using a simple Wall Mail Job:
- Create a mail formula rule with the formula provided above:
- Create a new Wall Mail Job, set the priority, and include the rule you have just created in "Dependence on positive rules" under the "Basics" tab:
- Define the desired reaction under the "Operations" tab:
- Define the desired quarantine configuration under the "Misc." tab:
There is nothing wrong with delivery status notifications per se. They are described and their use precisely defined in the relevant RfCs. However, the techniques currently used by spammers mean that more detailed knowledge of DSN mechanisms and how to handle DSNs is required. At the same time, you need to configure your own e-mail server to ensure that you yourself do not send NDRs that are generated by an incorrect sender (the spammer) and delivered to an unknowing recipient.
In our training sessions and workshops, we look into the various spam techniques in great detail, including of course non-delivery reports and their origin. This knowledge will enable you to formulate a suitable anti-spam concept and configure your e-mail server so that you don't become an unwitting member of the spammer community.
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