Improved Spam Management with Greylisting

You may have noticed a recent sharp reduction in the amount of unwanted junk mail, known as spam. This is because of the introduction of a spam management technique known as "greylisting". Some members have experienced spam reductions of 90% or more - but the amount will vary from member to member.

We have had lots of positive feedback since this was introduced and also some questions from members. Below are some answers to frequently asked questions.

Greylisting FAQs

Q1. Wow - a reduction in spam of 90%. How has that miracle come about?

A.   Greylisting is a smart new way of working out whether a message is coming from a genuine sender or from a spammer. That allows delivery of spam to be almost entirely prevented.

Q2. How do you manage that when it hasn't been possible before?

A. The idea is to take advantage of an Internet regulation for the handling of mail which requires that if a message is temporarily rejected it must be re-sent.

Legitimate senders comply with that regulation, spammers - who are only interested in raw speed - mostly don't.

Q3. So you reject my mail? I don't like the sound of that!

A. What happens is this. If we get a message for you, we initially tell the other server that your mailbox is temporarily unavailable. But at the same time we record some key details about the message so that when the message is re-sent we will know we have seen it before.

The other server, as required by Internet regulations, re-sends the message (usually in about 10 minutes) and this time we accept it.

We also keep a note of the message details so that any further message of the same type can be accepted immediately. (Of course, if the message had been from a spammer it may not be re-sent and that would be one spam message you would not receive.)

If you are interested in more details about how greylisting works, Evan Harris's whitepaper on greylisting is a good place to start.

Q4. So that's why you are saying that messages may be delayed an average of 10 minutes?

A. Yes, a message may be delayed by about 10 minutes, but the majority of legitimate messages will be accepted without delay. The greylisting system has an automatic whitelisting facility. Once we know that a particular server is genuine, it gets whitelisted for all users across the system. That means that any mail from those servers will be accepted straightaway.

Q5. Won't spammers simply change their tactics to adapt to greylisting?

A. They may. But for them to do that, they will have to accept a big reduction in the speed they can send out messages. That won't be very good news. But we'll have to wait and see.

Q6. I depend on my mail - I just can't afford to miss any messages. Can you absolutely guarantee that legitimate mail won't be permanently rejected?

A. No we can't, but it is very unlikely that legitimate mail would not be delivered due to greylisting. There are various safeguards built into it designed to reduce that possibility but almost any anti-spam system carries some risk. However, that risk is minimal.

Users should keep in mind that email was never intended to be a totally "bullet proof" delivery system.

If someone has had problems sending you email it is more likely to be for another reason. For assistance in finding out why you might not be getting some mail you can log a request for help from our Internet Help team.