Desktop and Server Virtualisation Specialist 

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Precedence Technologies Ltd
Technology House, 36a Union Lane
Cambridge, CB4 1QB, United Kingdom
T: +44 (0)8456 446 800 / +44 (0)1223 359900

Do you provide any unsolicited commercial email (a.k.a. spam) filtering?

Yes. We use a number of tools to stop the reception of spam email.


When valid emails are sent, but the destination mail server is temporarily too busy (or otherwise unavailable), they will sit in a queue on an intermediate server which will periodically retry delivering the mail. In this way, temporary downtime on the destination server will not stop mail being reliably delivered. Greylisting uses this feature to stop large amounts of spam.

When someone first sends you an email, their server will be told to try again later. A note is kept so that when they try again (after a certain greylist period has elapsed), the mail will be accepted immediately. As a valid mail server will always try again, the mail will be delivered safely. Spam mail is very rarely sent via valid mail servers (as doing so would make it easy to track) and as the spammers are sending millions of unsolicited mails, they will not bother trying to remember to track and retry any mails which cannot be immediately delivered. The sending email address, the recipient email address and the server they send from are linked together when greylisting, so only a retry from the same server and to and from the same addresses will be allowed. Specifically, this means that if someone sends an email to one of your email addresses and gets allowed through, if they send to a different address, they will get queued by greylisting again.

Senders with valid SPF (Sender Policy Framework) records set up will not be greylisted, as long as the SPF records are not configured to be valid for the whole world (i.e. not +all). SPF has always been somewhat controversial and does not work well with forwarded mails, so we do not reject mail with invalid SPF records, however we will greylist it for longer.

Enabling greylisting means a small delay the first time someone first sends you an email, but blocks a very high proportion of junk mail. We do NOT enable greylisting by default on email accounts because we feel our customers should be aware of the time delay aspect before proceeding. If you wish to have greylisting enabled, please contact us and we'll enable it straight away. We can even leave certain addresses without greylisting (e.g. support addresses) if you need to ensure you can be contacted immediately under some circumstances.

Adaptive filtering

All emails received by our servers passes through SpamAssassin which analyses the content and format of the message before giving it a numerical spam rating. Mails with a high spam rating will be rejected whereas suspicious, but not definite, spams will be flagged as [***SPAM***], but still delivered.


We use The Spam and Open Relay Blocking System (SORBS) to filter all incoming emails. An open relay is a mailserver on the Internet that will allow anybody in the world to send mail to anyone else in the world using it. This is completely unnecessary; all mail should be sent out via your ISP's mail relay. Therefore all mail will be rejected from mail servers on the Internet that are misconfigured to allow them to propagate spam. There is a small chance that this will stop email being sent by valid users of that mail server. If this is affecting you, please contact your ISP and refer them to the SORBS web pages.

We have recently started using the blocklist from Spamhaus. Spamhaus tracks the Internet's worst spammers, known spam gangs and spam support services. It works with ISPs and law enforcement agencies to identify and remove persistent spammers from the Internet.

In addition, we also block certain domains and IP addresses that we have personal experience of receiving spam from.

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