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Does greylisting work? Will it?


chrislott

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My ISP offers greylisting for coping with spam. The way they describe this, it sounds like their SMTP server simply responds to every first delivery attempt with some kind of "too busy, try again later" status, and accepts every second attempt. This presumes that spammers ignore the return codes, and valid email comes from store-and-forward systems that will keep trying. It seems like a great idea but I bet there's a catch, and I don't just mean waiting the extra 10 min or whatever the delay is. Any one have comments or experience with this? If it's a solid approach, has Spamcop ever tried it? Please advise, thanks.

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Search on it ... you will find many places where it has an impact ... one of which is mail from the SpamCop system itself ... folks trying to set up their accounts for the MailHost configuration for one example ...

Does/Did SpamCop use it - No

The Challenge/Response thing touted by several companies these days as "the ultimate spam solution" was dropped years ago by the SpamCop system as a failed experiment ....

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I'm quite certain that greylisting is not a challenge-response scheme at the user level. I think instead it's a mailer-daemon to mailer-daemon thing.

What impact does greylisting have on Spamcop mail host config?? How does greylisting have an impact on the SpamCop system?

Very curious. Thanks.

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Yes, I understand grey-listing .. I just thought I'd be nice and add extra data into the response, thus the inclusion of the Challenge/Response (which actually can be seen as much the same thing, one dealing at user level, the other at server level ..)

If you are "really" curious, you have the search terms involved, I pointed you to the Forum section that some impact had been documented in ... and I do see the suggestion "Search on it" still showing in my last post ...

Bottom line, sensitivities being that the SpamCop system will not be seen as a spamming system, so if e-mail is sent and is rejected, why re-try? Decisions on this are made by Julian, so if you want to debate the issue, you'll have to take it up with him.

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When Wazoo wrote "search on it" I went to google and found quite a bit. Didn't quite see any hints in the first follow up about SC forums, so didn't think of that. For anyone who is still following, here is a thread from a SC forum about mailhost config and greylisting:

http://forum.spamcop.net/forums/index.php?showtopic=1852

The connection to the MailHost issue is as follows: apparently as part of establishing a MailHost, SC sends a probe email, and if that probe email is not immediately accepted, the MailHost is not set up properly. Greylisting causes the first attempt to fail.

I don't know if the comments in that thread are relevant to the behavior of email accepted by SC's webmail system for delivery to the wide world. But "bottom line" as Wazoo says, with many ISPs greylisting, I hope Spamcop honors the intent of the email RFCs, and if it receives a 450 response on an outbound delivery attempt, tries again later.

Not interested in debating.

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Well, if you 'started' with a Google, then you should have come across a fair number of issues ... SMTP error codes 4xx are generally supposed to be "temporary" failures (5xx suggesting 'permanent' errors) ... however, not all e-mail server admins read the documentation ...

Another issue .. e-mail admin sets the grey-listing service up expecting to see a re-try within 10 minutes .. however, the 'sendig' server doesn't get around to re-trying for 30 minutes ... question is, how many attempts are going to be made on that delivery before either system deciding to handle the situation .. the recipient system deciding that it's under attack for instance, the sending system finally saying 'heck with it, the other system is broken bigtime' .... by the way, spammer work-around? ... send the spew twice (no new revealed secret here) ... cheering up the non-grey-listing-ISP-users even more .... you are right, debate isn't really necessary ..

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