spambots and dictionary attacks

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I would like to hear from anyone that has successfully blocked
spambots or dictionary attacks without the need of another server in
between your mailserver and the senders.
The mailserver on my end is exim and it is actually a virtual server,
so i cannot really edit the exim.conf file, but have access to access,
virtusertable, trustedusers and sendmail.cw.

regards
rowland


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