First, please note that the Spam Auto-Filtering function does not have effect on those email originated from the central email servers (i.e. staff, student, alumni, and EBS mail servers). i.e. This function only handles email sent from external sites, or from some departmental mail servers who route their email through the incoming mail gateway.
On the incoming mail gateway, all emails are scanned by a spam-detection software. Each email is tagged with the "spam level", which is a number representing the likelihood that the email is spam, in its mail headers.
The "spam level" is indicated in the "X-Spam-Level" header line of an email. A greater value (e.g. 9) means that the email has a higher probability of being spam. Conversely, a smaller value (e.g. 1) means that the email has a relatively lower probability of being spam. This mail header line usually appears only when the full header of the email is displayed. If you want to know how to display the full header of an email, please refer to this Email FAQ.
By enabling the Spam Auto-Filtering function, you can make use of this automatic spam-detection mechanism to filter junk mail based on this "spam level" by choosing an appropriate spam threshold. Please refer to here for the detailed procedure of enabling this function.
Please be aware that no spam-detection software can be 100% accurate. Two types of errors may occur in any automatic spam identification system:
False positives
False negatives
Return to University In-house Email Service FAQ page
IT.ServiceDesk@cityu.edu.hk
