What is proper RHS value in virtual to invalidate afully-qualified address?

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What is proper RHS value in virtual to invalida...
\ Jim Long (16 Apr 2007)
. \ (Wietse Venema) (16 Apr 2007)

4 msg	Postfix on Solaris

Subject:	What is proper RHS value in virtual to invalidate afully-qualified address?
Group:	Postfix-users
From:	Jim Long
Date:	16 Apr 2007

And if I may ask the meta-question,

What string do I have to put into Google in order to avoid
having to ask the mailing list:

"How do I craft an entry in etc/postfix/virtual to invalidate
an email address that would otherwise be delivered locally?"

user is a local UNIX account which receives mail as
user. I do not wish it to receive mail addressed
to user. local.example.com is in mydestination.
virtual.example.com is not.

etc/postfix/virtual:

user user
user ???