[Mimedefang] Rejecting Mails for More Than 3 Unknown Users
Joseph Brennan
brennan at columbia.edu
Tue Mar 27 08:40:05 EDT 2007
--On Tuesday, March 27, 2007 13:10 +0800 imacat <imacat at mail.imacat.idv.tw>
wrote:
> Dear all,
>
> Hi. This is imacat from Taiwan. Is it possible to reject mails for
> more than 3 unknown users, to fight against dictionary attacks?
>
> I have thought about this in 2 ways,
>
> 1. In filter_recipient(), if there are already 3 unknown recipients,
> drop all the following recipients.
Put this in sendmail.mc and generate sendmail.cf. Test it.
LOCAL_RULESETS
SLocal_check_rcpt
R$* $: $1 $| $( arith l $@ $&{nbadrcpts} $@ 3 $)
R$* $| FALSE $#error $: 450 Too many bad recipients
This says, after we have seen 3 bad recipients, we give 450 "Too many
bad recipients" to all remaining recipients.
Joseph Brennan
Lead Email Systems Engineer
Columbia University Information Technology
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