[Postfix-es] Correo externo no funciona

[Roberto Carriquiry]

Estimados, tengo el siguiente problema. Tengo un servidor postfix
configurado. Puede recibir correos desde afuera y enviar correos a todos los
usuarios internos. Sin embargo cuando intento enviar un correo a una cuenta
externa me rebota. En el mail.log aparece:

May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql: successful
connection to host localhost
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql: successful query
from host localhost
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql_lookup: retrieved 0
rows
May  4 18:30:58 correo postfix/smtpd[12799]: maps_find:
virtual_mailbox_maps: usuario en externo.com: not found
May  4 18:30:58 correo postfix/smtpd[12799]: match_string: externo.com ~?
correo
May  4 18:30:58 correo postfix/smtpd[12799]: match_string: externo.com ~?
localhost.localdomain
May  4 18:30:58 correo postfix/smtpd[12799]: match_string: externo.com ~?
localhost
May  4 18:30:58 correo postfix/smtpd[12799]: match_list_match: externo.com:
no match
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql_lookup using sql
query: select maildir from users where address = '@externo.com'
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql_get_active: found
active connection to host localhost
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql: successful query
from host localhost
May  4 18:30:58 correo postfix/smtpd[12799]: dict_mysql_lookup: retrieved 0
rows
May  4 18:30:58 correo postfix/smtpd[12799]: maps_find:
virtual_mailbox_maps: @externo.com: not found
May  4 18:30:58 correo postfix/smtpd[12799]: mail_addr_find:
usuario en externo.com -> (not found)
May  4 18:30:58 correo postfix/smtpd[12799]: NOQUEUE: reject: RCPT from
unknown[192.168.7.82]: 550 <usuario en externo.com>: Recipient address
rejected: User unknown in virtual mailbox table;
from=<originario en interno.com> to=<usuario en externo.com> proto=ESMTP
helo=<lolo.com>


Lo que SUPONGO que está pasando es que está intentando entregar el correo
externo como si fuera un dominio virtual. Pero no he logrado encontrar donde
puede ser que este eso configurado. 
Supuse que seteando el default_transport a smtp


Mi postconf -n es:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
config_directory = /etc/postfix
debug_peer_level = 2
debug_peer_list = 127.0.0.1
default_transport = smtp
inet_interfaces = all
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
message_size_limit = 20480000
mydestination = correo, localhost.localdomain, localhost
myhostname = correo.interno.com
mynetworks = 127.0.0.0/8, 192.168.7.0/24
myorigin = /etc/mailname
recipient_delimiter = +
relayhost =
smtpd_banner = ESMTP $mail_name (Debian/GNU)
smtpd_recipient_restrictions = permit_mynetworks,
permit_sasl_authenticated,      reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_security_options = noanonymous
transport_maps = mysql:/etc/postfix/transport.cf
virtual_gid_maps = mysql:/etc/postfix/gids.cf
virtual_mailbox_base = /var/mail
virtual_mailbox_domains = mysql:/etc/postfix/virtual_domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql_virt.cf
virtual_uid_maps = mysql:/etc/postfix/uids.cf