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.
Greylisting
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.
We do not currently block mail with SPF (Sender Policy Framework) records set up, though given that SPF is not very well thought through, we may change this policy in future.
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.
Blacklists
We use the Open Relay Database 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 ISPs 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 Open Relay Database web pages.
We also use the services provided by NJABL (Not Just Another Bogus List) and the Composite Blocking List. These are often complementary to the Open Relay Database as they have listings for known spammers, open proxies as well as dial-up users. All dial-up users must use their ISP's SMTP servers when sending out mail, not doing so will mean you stand a good chance of your mail being rejected.
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 Intenet.
In addition, we also block certain domains and IP addresses that we have experience of receiving spam from.
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