Exmap is a an extremely useful tool, which will automatically generate a Visio diagram of your Exchange Organization. It may take a little trial and error to get the desired layout, however this tool can save a tremendous amount of time for a large Exchange Topology scenario.
It can run on NT 4.0, however the ADSI support package must be installed in order for it to work properly. You will also need your site services account and password, as well as LDAP enabled on at least one server in your Exchange Organization.
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