misdelivery of mail to user@virtual to user@domain

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misdelivery of mail to user@virtual to user@domain
\ Gary Casterline (24 Jul 2007)
. \ mouss (24 Jul 2007)
. . \ Gary Casterline (24 Jul 2007)
. . . \ mouss (25 Jul 2007)
. . . \ LuKreme (26 Jul 2007)

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Subject:	misdelivery of mail to user@virtual to user@domain
Group:	Postfix-users
From:	Gary Casterline
Date:	24 Jul 2007

I'm having mail sent to a virtual address mis-delivered to an
actual unix account with the same name.

in main.cf:
virtual_alias_domains = hash:$config_directory/virtual_alias_domains
virtual_alias_maps = hash:$config_directory/virtual_alias_maps

in /etc/postfix/virtual_alias_domains:
virtual.domain.tld virtual

% postmap -q info /etc/postfix/virtual_alias_maps
user

Test messages to info go to user as expected.
However, *sometimes* mail addressed to info gets
delivered to info, where info is an actual unix account on
domain.tld.

Anyone see where I've missed something obvious?
Where might I best enable debugging to find out why?

Thanks,

_Gary