Greylisting and new posters

Erik Norgaard norgaard at
Sat May 30 08:20:14 UTC 2009

Mel Flynn wrote:

> Is it possible to:
> a) Put a big-red-blink-popup-attentiongrabbing monster text into the 
> subscription page about first posts being delayed with a link to greylisting?
> b) Hash the bodies of greylisted messages and reject / discard if the same 
> body with a different msg id is being received?
> I'd be happy to contribute to b) if it is thought that the incoming mailer can 
> handle the hashing and storage of this information.

Hi, ok sorry about that mail yesterday :) I've been off the list for 
some time.

It would be great if the confirmation mail and the subscription page 
would include the message:

"After confirming/activating your subscription your first mail may be 
delayed X minutes due to grey listing"

Also, it would be great to have a descriptive error message, rather than 

  450 4.7.1 <questions at>: Recipient address rejected: Service 
is unavailable (in reply to RCPT TO command))

This text message indicates an error in the recipients end, while the 
450 status indicates it's temporary.

IIRC the postgrey port will provide a message along the lines "sender 
postgreyed X seconds, see website for more information."

Your option b) won't work: you propose to reply with a 2XX (OK) or 5XX 
(rejected, don't try again) if subscriber sends the message again.

Problem is that the server after receiving the 450 error will retry 
after some time and this may be before the sender is white listed. So if 
you implement the solution you propose you risk that the original 
message is either discarded or rejected.

So, you need to come up with an idea of how to distinguish between the 
server resending the same message and the subscriber resending the same 
message. If anything, I believe it's most likely that the subscriber 
will not send the exact same message, missing some blanks or double 
signature line etc...

Now, you could take an active approach, when a subscriber's first 
message is grey listed, send an automatic reply that the message is grey 
listed for X seconds.

But, then you have the problem that these auto replies will also be sent 
to innocent people who are being impersonated by some spammer, or to 
non-existing mail addresses which will generate loads of error messages.

Question: Did grey listing actually reduce the amount of spam on the 
list? I eventually dumped it as it caused more problems than it solved.

BR, Erik
Erik Nørgaard
Ph: +34.666334818/+34.915211157        

More information about the freebsd-questions mailing list