What is stopping postfix from delivering mail to the local transport agent?

I have the following settings ( as grabbed from my postconf -n output)

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
content_filter = smtp-amavis:[127.0.0.1]:10024
inet_interfaces = all
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
maximal_backoff_time = 8000s
maximal_queue_lifetime = 7d
minimal_backoff_time = 1000s
mydestination = $mydomain, localhost.$mydomain, localhost
myhostname = //redacted
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter = +
relayhost =
smtp_helo_timeout = 60s
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_hard_error_limit = 12
smtpd_recipient_limit = 10
smtpd_sasl_auth_enable = yes
smtpd_sasl_authenticated_header = yes
smtpd_sasl_local_domain =
smtpd_sasl_path = private/auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_soft_error_limit = 3
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
unknown_local_recipient_reject_code = 450
virtual_alias_maps = mysql:/etc/postfix/mysql_virtual_alias_maps.cf, mysql:/etc/postfix/mysql_virtual_alias_domainaliases_maps.cf
virtual_gid_maps = static:8
virtual_mailbox_base = /var/vmail
virtual_mailbox_domains = mysql:/etc/postfix/mysql_virtual_domains_maps.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql_virtual_mailbox_maps.cf, mysql:/etc/postfix/mysql_virtual_mailbox_domainaliases_maps.cf
virtual_transport = virtual
virtual_uid_maps = static:5000
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_overquota_bounce=yes
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_mailbox_limit_maps=mysql:/etc/postfix/mysql_virtual_mailbox_limit_maps.cf
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_maildir_limit_message=Sorry, the your maildir has overdrawn your diskspace quota, please free up some of spaces of your mailbox try again.
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_create_maildirsize=yes
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_mailbox_extended=yes
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_mailbox_limit_override=yes
postconf: warning: /etc/postfix/main.cf: unused parameter: smtpd_relay_restrictions=reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_recipient, reject_unauth_destination, check_policy_service inet:127.0.0.1:10023, permit

I am nwe to mail server configurations but as I understand it from this message: status=deferred (mail transport unavailable) It means it can't deliver to the LDA. I am using postifx 2.9.6 on ubuntu 12.04 with dovecot 2.0.19

edit : mail arrival log

Jun 12 12:18:59 mailserve postfix/smtpd[1215]: warning: database /etc/aliases.db is older than source file /etc/aliases
Jun 12 12:19:00 mailserve postfix/smtpd[1215]: connect from redacted
Jun 12 12:19:00 mailserve postfix/smtpd[1215]: 6788268E01E9: client=redacted
Jun 12 12:19:00 mailserve postfix/cleanup[1196]: 6788268E01E9: message-id=<[email protected]>
Jun 12 12:19:00 mailserve postfix/qmgr[678]: 6788268E01E9: from=<redacted>, size=17120, nrcpt=1 (queue active)
Jun 12 12:19:00 mailserve postfix/qmgr[678]: warning: connect to transport private/smtp-amavis: No such file or directory
Jun 12 12:19:00 mailserve postfix/smtpd[1215]: disconnect from redacted
Jun 12 12:19:01 mailserve postfix/error[1223]: 6788268E01E9: to=<redacted>, relay=none, delay=0.75, delays=0.38/0/0/0.36, dsn=4.3.0, status=deferred (mail transport unavailable)