Remote SMTP authentication audit tool?

["Byron Pezan" <mbp@xxxxxxxxxx>]

I have found that several spammers are exploiting weak or non-existent 
passwords on some MS Exchange servers using external SMTP authentication.  I 
have also found out (through Tech Net) how to turn on logging for SMTP 
authentication and see what account is being abused for this purpose.  However, 
this is too reactive of an approach.  Does anyone know of a way or a tool to 
audit existing servers for weak or non-existent SMTP passwords?

byron