[MAILSCANNER] Reverse NDR attack.How to combat ? Any ideas ?

[Matt Kettler]

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Venkata Achanta wrote:
> Thanks Matt.didnt make sense until it became a reality on my mail servers 
> this week. I agree with you 100%. 
> 
> Now if i go the route of accepting e-mail for only valid users, how do i 
> mitigate the risk of Directory Harvest attack on a setup like mine ?can you 
> throw some light on it as well ?

What's your outside MTA? Sendmail?

Try this sendmail.mc config option to deal with dictionary attacks:

#after 10 invalid recipients, start slowing them down with
#1 second sleeps, makes dictionary attacks very slow

define(`confBAD_RCPT_THROTTLE',10)

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