Anti-spam and Anti-virus measures

All messages are scanned for viruses, worms, etc, using Sophos Anti-virus software. If a virus is detected which appears on a list of those known to forge sender addresses, the message is simply discarded, as rejecting it would cause an error message to be sent to an innocent third party. Otherwise, the message is rejected.

Messages are scanned using the open-source ClamAV anti-virus scanner. It also can detect some classes of "phishing" messages (malicious messages attempting to fool victims into entering their financial details into bogus websites).

Messages are then passed for onward delivery and further checking within Microsoft 365 Defender that may quarantine dangerous messages for review.

Spam filtering with SpamAssassin

SpamAssassin is a popular open-source software package which applies a variety of textual and other tests to messages in order to estimate the likelihood that they are spam. This likelihood is represented as a number, the spam score. So SpamAssassin assigns a score to each message it sees, which can subsequently be used to determine the message's disposition.

SpamAssassin is run on the main University mail relays. It scans all messages coming in to the mail relays from networks outside the University. Messages from within the University's network are not scanned. It adds headers to a scanned message containing indications of the spam score assigned to it, and the mail system then continues processing the message as normal.

The threshold

The main control over the spam filtering is a number called the threshold. Messages rated with a score equal to or greater than the threshold are filed in the likely spam folder; messages rated less than the threshold are not affected, and will be delivered to your inbox (unless there are subsequent filtering rules in place which might affect it).

At any given threshold there is always a chance that a spam message is filed in your inbox (a false negative) and a chance that a nonspam is filed in the likely spam folder (a false positive). If you increase the filtering threshold, the chance of false negatives increases, so more spam gets through to your inbox. At the same time, the chance of false positives decreases, so less nonspam mail is filed along with the spam.

Where the threshold should be set depends on the sort of email that each user receives. If you receive mail that tends to score highly, such as HTML-formatted newsletters, commercial announcements, and so on, you may prefer a higher threshold to allow this mail through to your inbox while accepting that a higher amount of spam will get through with it. If you receive only relatively "clean" mail, you may prefer a lower threshold. You may also prefer a lower threshold if you are prepared to check your likely spam folder often, while a higher threshold would allow you to check it less often.

How to filter spam based on your threshold score

You can setup a spam filter on staffmail or Student Mail service using the webmail interface:

People using the Office 365 mail service should setup their spam filter using Outlook: