uid ruim 8 em virtual_uid_maps

Falha ao enviar e-mail. Os logs mostram este erro:

warning: recipient [email protected]: bad uid 8 in virtual_uid_maps

Configurações relevantes em main.cf:

local_recipient_maps =
virtual_uid_maps = static:8
virtual_gid_maps = static:12
transport_maps = pgsql:/etc/postfix/pgsql/transport.cf
virtual_mailbox_base = /var/spool/mail
virtual_mailbox_maps = pgsql:/etc/postfix/pgsql/mailboxes.cf
virtual_maps = pgsql:/etc/postfix/pgsql/virtual.cf

/var/spool/mail pertence a mail:mail:

root@gentooserver ~ # ls -la /var/spool/mail
total 4
drwxrwsr-t 1 mail mail 92 Apr 11 19:00 .
drwxr-xr-x 1 root root 68 Nov 29 17:05 ..
-rw------- 1 mail mail 31 Apr 11 18:51 .bash_history
-rw-r--r-- 1 mail mail  0 Nov 29 17:05 .keep_net-mail_mailbase-0
drwx--S--- 1 mail mail 18 Apr 11 19:00 .maildir

mail tem um UID de 8:

root@gentooserver ~ # cat /etc/passwd | grep mail
nullmail:x:88:88:added by portage for nullmailer:/var/spool/nullmailer:/sbin/nologin
mail:x:8:12:added by portage for mailbase:/var/spool/mail:/sbin/nologin
postmaster:x:14:232:added by portage for mailbase:/var/spool/mail:/sbin/nologin

Qual é o problema?