Re: [exim] Greylisting

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Autor: Ryan Tracey
Data:  
Para: Carl Inglis
CC: exim-users
Assunto: Re: [exim] Greylisting
Hi

Carl Inglis wrote:
> When I introduced greylisting here it cut the spam down by 97%.
> Unfortunately I have a number of users who started complaining about the
> delay and that killed the project.


I met with similar resistance so I ended up doing something which I think works quite well.  You could limit greylisting to those hosts that act somewhat like spammers but you aren't quite sure enough to drop/deny them outright.   I posted an extract from my acls a few weeks ago. Basically, I set acl_cX for certain condions like failures on helo and reverse_host_lookup verification, or appearance on a RBL. Then at acl_rcpt I look at acl_cX and greylist if those variables have anything assigned to them.    You may still end up greylisting a valid sender and not greylisting a spammer (who happens not to be on a RBL and has perfect dns entries and says helo nicely) but, by and large, you will stop a lot of spam.   Of course, I force greylisting to occur for all aliases and lists that are heavily spammed.   


I have also tried greylisting emails without message_ids, etc., at acl_data and use a generic recipient instead of $local_part@$domain.    


Hope that helps.

Cheers,
Ryan