[Mimedefang] Blocking Dictionary Attacks

Les Mikesell les at futuresource.com
Tue Jun 9 10:38:08 EDT 2009

afo cliff wrote:
>>>> Matt Garretson wrote:
>>>>> afo cliff wrote:
>>>>>> @mydomain.com bitbucket
>>>>> You can also do something like this in your virtusertable:
>>>>> @mydomain.com  error:5.1.1:550 User unknown
>>>>> Then, you won't need the bitbucket alias.
>>>>> See http://www.sendmail.org/m4/features.html
> Yes thanks, I tried that, the down side for me is that it sends a
> "User Unknown" reject notification, which I'm trying to avoid.  I
> don't want my server to waste time sending 10,000 rejects to a zombie
> somewhere.

You have that backwards - it's much, much faster to send a '5xx' failure 
response in the SMTP conversation before accepting any data.   Also, by 
accepting, you'll convince the sender that the addresses are legitimate 
and they'll end up on lists that are re-used for years - but it is 
probably already too late for that.

   Les Mikesell
    lesmikesell at gmail.com

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