==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.2
- Linux/BSD distribution name and version: Centos 6.7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): Mysql
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- Related log if you're reporting an issue:
====

When mails are sent to the user@aliasdomain.tld a "550 5.1.1 Recipient address rejected: User unknown in virtual mailbox table" occur.

We have create an entry in alias_domain table of the vmail database with those datas :

alias_domain     target_domain created                     modified                 active
aliasdomain.tld ourdomain.tlf   2016-02-03 00:00:00 0000-00-00 00:00:00 1

our postconf result :

alias_database = hash:/etc/postfix/aliases
alias_maps = hash:/etc/postfix/aliases
allow_min_user = no
allow_percent_hack = no
biff = no
bounce_queue_lifetime = 4h
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
config_directory = /etc/postfix
content_filter = smtp-amavis:[127.0.0.1]:10024
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5
delay_warning_time = 0h
disable_vrfy_command = yes
dovecot_destination_recipient_limit = 1
enable_original_recipient = no
home_mailbox = Maildir/
html_directory = no
inet_interfaces = all
inet_protocols = ipv4
lmtp_tls_mandatory_protocols = !SSLv2 !SSLv3
lmtp_tls_protocols = !SSLv2 !SSLv3
mail_owner = postfix
mailbox_command = /usr/libexec/dovecot/deliver
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
maximal_backoff_time = 4000s
maximal_queue_lifetime = 4h
message_size_limit = 20971520
minimal_backoff_time = 300s
mydestination = $myhostname, localhost, localhost.localdomain
mydomain = *********************
myhostname = ********************
mynetworks = 127.0.0.1, 5.39.77.51
mynetworks_style = host
myorigin = *******************
newaliases_path = /usr/bin/newaliases.postfix
proxy_read_maps = $canonical_maps $lmtp_generic_maps $local_recipient_maps $mydestination $mynetworks $recipient_bcc_maps $recipient_canonical_maps $relay_domains $relay_recipient_maps $relocated_maps $sender_bcc_maps $sender_canonical_maps $smtp_generic_maps $smtpd_sender_login_maps $transport_maps $virtual_alias_domains $virtual_alias_maps $virtual_mailbox_domains $virtual_mailbox_maps $smtpd_sender_restrictions
queue_directory = /var/spool/postfix
queue_run_delay = 300s
readme_directory = /usr/share/doc/postfix-2.11.0/README_FILES
recipient_bcc_maps = proxy:mysql:/etc/postfix/mysql/recipient_bcc_maps_user.cf, proxy:mysql:/etc/postfix/mysql/recipient_bcc_maps_domain.cf
recipient_delimiter = +
relay_domains = $mydestination, proxy:mysql:/etc/postfix/mysql/relay_domains.cf
sample_directory = /usr/share/doc/postfix-2.11.0/samples
sender_bcc_maps = proxy:mysql:/etc/postfix/mysql/sender_bcc_maps_user.cf, proxy:mysql:/etc/postfix/mysql/sender_bcc_maps_domain.cf
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtp-amavis_destination_recipient_limit = 1
smtp_data_init_timeout = 240s
smtp_data_xfer_timeout = 600s
smtp_tls_loglevel = 0
smtp_tls_mandatory_protocols = !SSLv2 !SSLv3
smtp_tls_note_starttls_offer = yes
smtp_tls_protocols = !SSLv2 !SSLv3
smtp_tls_security_level = may
smtpd_data_restrictions = reject_unauth_pipelining
smtpd_delay_reject = yes
smtpd_end_of_data_restrictions = check_policy_service inet:127.0.0.1:7777, check_policy_service inet:127.0.0.1:10031,
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_helo_hostname, reject_invalid_helo_hostname, check_helo_access pcre:/etc/postfix/helo_access.pcre
smtpd_recipient_restrictions = reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unlisted_recipient, check_policy_service inet:127.0.0.1:7777, permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination, reject_non_fqdn_helo_hostname, reject_invalid_helo_hostname, check_policy_service inet:[127.0.0.1]:10031, reject_rbl_client all.spam-rbl.fr
smtpd_reject_unlisted_recipient = yes
smtpd_reject_unlisted_sender = yes
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
smtpd_sasl_path = private/dovecot-auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_sender_login_maps = proxy:mysql:/etc/postfix/mysql/sender_login_maps.cf
smtpd_sender_restrictions = reject_unknown_sender_domain, reject_non_fqdn_sender, reject_unlisted_sender, permit_mynetworks, reject_unauthenticated_sender_login_mismatch, permit_sasl_authenticated
smtpd_tls_cert_file = /etc/postfix/tls/smtpd.pem
smtpd_tls_dh1024_param_file = /etc/pki/tls/dhparams.pem
smtpd_tls_key_file = /etc/postfix/tls/smtpd.pem
smtpd_tls_loglevel = 0
smtpd_tls_mandatory_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA
smtpd_tls_mandatory_protocols = !SSLv2 !SSLv3
smtpd_tls_protocols = !SSLv2 !SSLv3
smtpd_tls_security_level = may
strict_rfc821_envelopes = yes
swap_bangpath = no
tls_random_source = dev:/dev/urandom
transport_maps = proxy:mysql:/etc/postfix/mysql/transport_maps_user.cf, proxy:mysql:/etc/postfix/mysql/transport_maps_domain.cf, hash:/etc/postfix/transport
unknown_local_recipient_reject_code = 550
virtual_alias_domains =
virtual_alias_maps = proxy:mysql:/etc/postfix/mysql/virtual_alias_maps.cf, proxy:mysql:/etc/postfix/mysql/domain_alias_maps.cf, proxy:mysql:/etc/postfix/mysql/catchall_maps.cf, proxy:mysql:/etc/postfix/mysql/domain_alias_catchall_maps.cf
virtual_gid_maps = static:2000
virtual_mailbox_base = /var/vmail
virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql/virtual_mailbox_domains.cf
virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql/virtual_mailbox_maps.cf
virtual_minimum_uid = 2000
virtual_transport = dovecot
virtual_uid_maps = static:2000

I don't see what we miss ....

Regards