Greylisting

[digp]

Is FM likely to add such a facility?

What are the pros and cons? Can anyone shed a light on this?


"MailSnare is please to add Greylisting to its growing repertoire of anti-spam capabilities. Greylisting has been undergoing beta testing since early July and has proven to be highly effective – especially in combination with SpamAssassin.

There is a technical description of greylisting and links to a number of related articles at http://www.greylisting.org but here is a brief description:

With greylisting enabled, the first time you receive a message from an unknown (i.e., non-whitelisted) user, our server tells the sending server “no thank you, please try again a little bit later”. The sending mail server waits a short period of time (generally less than an hour) and then automatically attempts to resend the message to us, at which point we then accept it the second time around. Since a sizable percentage of spam comes from hijacked systems and viruses that are not true mail servers, they are unable to queue or resend the message and the spam simply evaporates. "

[David]

Originally posted by digp
Is FM likely to add such a facility?

With greylisting enabled, the first time you receive a message from an unknown (i.e., non-whitelisted) user, our server tells the sending server “no thank you, please try again a little bit later

I would hope that greylisting would never be activated by default! Most of my mail is delivered by way of Listserv (who only attempt to deliver mail once)

[Madiver]

Originally posted by digp
Is FM likely to add such a facility?

What are the pros and cons? Can anyone shed a light on this?

Here are some of the pros and cons off the top of my head...I'm sure others will offer up more examples:

Cons:

1. When used by itself, it is not all that effective (in my experience)

2. The amount of time legitimate mail is delayed is dependent on the sending mail server, so it can range from a very short period of time to several days.

3. Some legitimate mail servers treat temporarily refused mail as a bounced message and do not requeue it. This does not seem to be all that common and Greylisting can be implemented to allow "white listing" these servers when known. However, it does represent a small risk (again, my opinion) and could potentially result in lost mail.

4. Some sending mail servers, send notifications to the sender that their message was temporarily refused. While this doesn't seem to be very common, when it does happen it often confuses the sender into thinking their message has been bounced. Use of white listing can also virtually eliminate this problem.

Pros:

1. When used in conjuction with SpamAssassin, it appears to be highly effective at reducing the overall amount of spam that does reach your inbox without increasing "false positives" - I don't have any real metrics on this but that has been my experience over the past 6 months.

2. Relatively simple and farily easy to understand approach to reducing spam


Anyway. that's my 2-cents worth I think greylisting is valuable as an additional spam fighting tool, but not something you would want to use all by itself unless you can tolerate a fair amount of spam still getting through to your inbox. I also think this is something that most people would want to be able to turn on or off at their discretion.

Mark