“Why does Nexus send me spam?”

We have had a spate of spam making it into Nexus mailboxes recently, provoking a flurry of discourse on the ITSS-Discuss mailing list. To be able to stop spam more effectively there are some checks that IT Support Staff can do with their users prior to logging support tickets.

Spam detection isn’t as simple as virus/malware detection: there isn’t the same definitive certainty one gets when a virus’ signature matches a message’s attachment. To conclusively determine if a message is spam requires an understanding of context and language that is currently still far in excess of a humble computer’s capabilities. There is also a personal aspect – one person’s spam message is another’s crucial information. So spam isn’t deleted, no matter how certain we can be that that’s what it is. Instead we allow you to personally set your own tolerance to spam. If you do this correctly it will determine what goes into ‘Junk’ and what goes into ‘Inbox’.

Firstly though, here’s what is going on with incoming email:

New messages arrive at OXMAIL and are scanned. Details of Oxmail’s processes can be found here: http://help.it.ox.ac.uk/email/scanning/index and here: https://help.it.ox.ac.uk/network/smtp/relay/index

OXMAIL then sends messages on to their destination, which might be Nexus, forwarded to a personal email address outside the University, or to a departmental server.

The spam score assigned by OXMAIL is translated directly into a Spam Confidence Level, or SCL. Each asterisk in the X-Oxmail-Spam-Level header is counted: the total becomes that message’s SCL. So this example ‘X-Oxmail-Spam-Level: *********’ would have an SCL of 9.

Nexus is able to automatically move spam messages into the Junk folder of your mailbox before you see them, but only if you tell it to do so. This is a two-stage process:

  1. Turn on the spam filter in OWA. This step often gets overlooked. Without doing this step any setting you apply won’t take effect. Instructions for doing this can be found here: https://help.it.ox.ac.uk/email/filter/index.
  2. Select your level of tolerance to spam. This is done via the SelfReg tool (https://register.it.ox.ac.uk/self/nexus).
    The higher the SCL is that you can accept, the fewer messages will be moved into Junk. The options equate to the following:
    OFF: All messages will go into your Inbox.
    LOW: Messages with an SCL above 7 will be moved to Junk.
    MEDIUM: Messages with an SCL above 5 will be moved to Junk.
    HIGH: Messages with an SCL above 3 will be moved to Junk.


The assessment of spamminess done by OXMAIL is logged, consistent, and repeatable. If two people are sent the same message, and have the same spam-filtering preference set, then the same thing should happen to that message for both people.

End-users’ applications aren’t so clear-cut. Each program can use widely differing technologies to assess spam and the software which scans it isn’t always the same version, even when the application is the same. Furthermore, messages that are moved to Junk by the email client application can’t be differentiated between a user choosing to move a message between folders or their software doing it for them. All that Nexus’ servers see is an end-user request for a message to be moved.

In other words Outlook, and others, can do a pretty good job of spotting and filtering spam after it’s delivered. But we can’t guarantee that your program won’t falsely-identify a genuine message as spam. We can’t guarantee that your experience will match that of the person next to you (do they update as often as you do?). We can’t see in our logs what process decided to move that message between folders.

By deactivating client-side spam filtering we can be sure that the only spam processing that does happen is recorded in message headers.  This gives us a fighting chance of diagnosing any issues with the process. If you do spam filtering in your application you are muddying the waters for us if things misbehave and you want us to help you to troubleshoot.


  1. Check that the user has set spam processing in SelfReg AND has turned on spam processing in OWA.
  2. Review the headers of an offending message to see what Spam Score it has been given.
  3. Verify if the user’s application software, or rules processing, or macros, or any other such process might be doing additional spam processing / filtering.
  4. Ensure that the end-user hasn’t configured a whitelist within their email application that is over-riding the spam-processing values they have set.
  5. Record the outcome of these tests in the details when you log a ticket for us to investigate why you are receiving spam to your inbox.



EDIT 1st August 2016:

In the case of a shared mailbox SelfReg does not currently allow you to alter the spam preference – it is limited to the currently-logged-on user. However the Nexus team can manually apply spam preference values for you if spam becomes an issue within a shared mailbox.

Posted in Uncategorized | Comments Off on “Why does Nexus send me spam?”

Comments are closed.