How to avoid dictionary attacks, from internal network?

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How to avoid dictionary attacks, from internal ...
\ Javier Togra A. (13 Nov 2007)
. \ Noel Jones (13 Nov 2007)
. \ Tony Earnshaw (13 Nov 2007)
. . \ MacShane, Tracy (13 Nov 2007)

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Subject:	How to avoid dictionary attacks, from internal network?
Group:	Postfix-users
From:	Javier Togra A.
Date:	13 Nov 2007

I have some customers rejecting mail from my Server.

They said:

denied after dictionary attack (in reply to RCPT TO command)

It seems to be a virus in my internal network sending mail to my customers.

Thanks.

Javier Togra A.

SEGINFO S. A.

Tel: 2390852 - 098480962