what is a user-oriented virtual-domain tables

[François Philippo]

I try to replace an interresting netscape messenger function with qmail.

auto-rewrite an email address and send it to the good server
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ex:
receive an email for [EMAIL PROTECTED]
rewrite to [EMAIL PROTECTED]
and sending it
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the best would be to works with ldap (like netscape)

I have found fastfoward. 
which works with an what is a user-oriented virtual-domain tables.
can someone send me an example of a such table?

thanx