Spam

  1.  How spam control works at the University
  2. The "SP? {Spam?}" tag
  3. Opting out of the spam control checks

We estimate that the University email system processes more than 1.5 million messages per day and as much as 95% may be rejected because it is spam or carries a virus.

1. How the filtering scheme works

Messages are rejected in real-time with a detailed "non-delivery report" (NDR) going back to the sender. This links to a possible explanation from the IT Service, which describes the most common reason for rejecting a message (usually blacklists). Thus, genuine sites (which may be on a blacklist through their own inexperience, or through accidental causes) are warned, and they can take action.

2. The SP? {Spam?} tag

All messages which come from sites which are not blacklisted have further filtering tests applied.

SpamAssassin anti-spam software analyses each message and gives it a "spam score". If the spam score is above a certain number, this means that the message is probably spam: it is marked with "SP? {Spam?" in the Subject line and is then passed on to the recipient. If the score is so high as to be almost certainly spam, the message is rejected in the same way as if the sender was found on a DNS blacklist.

Some spam messages will not be tagged because the type has not yet been identified to the mail scanning system, and analysis by SpamAssassin fails. However the tests are continually refined and updated, and examples of unrecognised spam can be used to "train" SpamAssassin to recognise similar types in future.

3. Opting out of the spam control checks

It is important to note that the anti-virus checks cannot be by-passed. They are are applied to all incoming and outgoing email. If you chose to opt out of the anti-spam filtering (see below), your email is still scanned for viruses, phishes and trojans.

The default action for a University email account is to filter all mail, rejecting messages that we strongly suspect are spam. This includes mail from blacklisted sites and messages with very high spam scores. We deliver all other messages but may tag certain messages we think might be spam but are uncertain about.

Q: Why would I want spam delivered?
A: There are a few users who prefer to analyse for themselves all email addressed to them. If you opt out of the spam filtering your messages are still scanned for viruses but all other messages, including spam, will be delivered to your mailbox. Blacklists are ignored. No delivered messages will be tagged with "SP?" in the Subject line.

Q: How do I opt-out to ensure all messages are delivered, including spam?
A: A web interface allows you to change settings. The two possible settings are:

  1. Default: reject mail that we strongly suspect is spam, but deliver all other messages. We maytag some messages that we are uncertain about, to alert you to possible spam.
  2. Switch off the default action, so that no mail is rejected.

Choose the second setting if you wish to opt-out.

Q: How do I change the settings?
A: Go to the Spam Filter Control web page: you need to authenticate with your IT Service login name.
(If you do not have an University user name then please email spammaster@ncl.ac.uk to change your rejection option.) The setting you make is applied from 1200 midnight, not immediately.

It is possible that tagged spam ("SP?") enters your mailbox because it has been addressed to an email alias of your address or to a mailing list (or similar) of which you are a member. If you want to change the defaults on behalf of other email addresses (for example a mailing list, or for a departmental mail address) please contact spammaster@ncl.ac.uk.