Solving the problem of non-delivery mails as spam
Spam senders misuse existing sender addresses to send their emails. If these emails are then addressed to non-existent recipients, the assumed sender subsequently receives a non-delivery report (NDR) for each non-deliverable email. This floods the inbox with unsolicited NDRs. The iQ.Suite 7 can be used to block these emails. How is this done? Read on to find out.
Step by Step:
- From iQ.Suite 7.0 upwards, SMTP sender and recipient data is used to check addresses. This enhances security, as SMTP information is much more tamper-proof than the data in the email file (the visible details in the email client).
- NDRs are sent with the SMTP sender "<>" by default. The email file typically contains the words "Postmaster" or "Mail Delivery System".
- This means that an address filter blocking emails from "<>" can be used as a solution.
- We thus use an iQ.Suite Wall email address filtering job to block the NDRs.
- The sender condition value "<>" is entered via the "user-defined addresses", and "internal sender/recipients" is entered for the recipients.
- This blocks all NDRs. It even blocks those created legitimately by the user’s own email server. The job therefore has an additional condition attached in order to allow these legitimate emails to get through.
- We query the field "from" via the "headers and values" condition. This field contains the sender address of the email file (not the SMTP sender). In the case of NDRs of the user`s own server, the user’s own server name and/or domain will be found in the “from” field.
- This information is now linked with the condition "doesn’t contain" and entered in the respective field.
- The result is a job that blocks all NDRs unless the system report comes from the user`s own server.
- Don`t forget to set your system to “copy to quarantine” to check the job - it`s essential that you do so. It’s a very easy way to test whether this job is blocking all the unsolicited mails.
- If there are other legitimate NDR senders, they can be added to the conditions.
