Postfix – Mail system is down

My Postfix mail log keeps giving me this error;

Oct  4 10:32:50 postfix/master[9760]: daemon started -- version 2.9.6, configuration /etc/postfix
Oct  4 10:32:54 postfix/postqueue[9885]: warning: Mail system is down -- accessing queue directly

I also can't flush the queue in postfix due to this error.
postconf -n output:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
config_directory = /etc/postfix
inet_interfaces = all
inet_protocols = ipv4
mailbox_size_limit = 0
mydestination = localhost
myhostname = host.example.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = /etc/mailname
readme_directory = no
recipient_delimiter = +
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reject_unauth_destination # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for # information on enabling SSL in the smtp client.
smtpd_sasl_auth_enable = yes
smtpd_sasl_path = private/auth
smtpd_sasl_type = dovecot
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/ssl/certs/dovecot.pem
smtpd_tls_key_file = /etc/ssl/private/dovecot.pem
smtpd_use_tls = yes
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_transport = lmtp:unix:private/dovecot-lmtp

My master.cf:

#
# Postfix master process configuration file.  For details on the format
# of the file, see the master(5) manual page (command: "man 5 master").
#
# Do not forget to execute "postfix reload" after editing this file.
#
# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       -       -       -       smtpd
#smtp      inet  n       -       -       -       1       postscreen
#smtpd     pass  -       -       -       -       -       smtpd
#dnsblog   unix  -       -       -       -       0       dnsblog
#tlsproxy  unix  -       -       -       -       0       tlsproxy
submission inet n       -       -       -       -       smtpd
#  -o syslog_name=postfix/submission
#  -o smtpd_tls_security_level=encrypt
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
#  -o milter_macro_daemon_name=ORIGINATING
smtps     inet  n       -       -       -       -       smtpd
#  -o syslog_name=postfix/smtps
#  -o smtpd_tls_wrappermode=yes
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
#  -o milter_macro_daemon_name=ORIGINATINGrelay   unix  -   -   n   -   -   smtp
flush     unix  n       -       n       1000?   0       flush
trace     unix  -   -   n   -   0   bounce
verify    unix  -   -   n   -   1   verify
proxymap  unix  -   -   n   -   -   proxymap
anvil     unix  -   -   n   -   1   anvil
scache    unix  -   -   n   -   1   scache
discard   unix  -   -   n   -   -   discard
tlsmgr    unix  -       -       n       1000?   1       tlsmgr
retry     unix  -       -       n       -       -       error
proxywrite unix -       -       n       -       1       proxymap

it worked fine before with local users, but when I set up mysql virtual users it stopped working.

output of ps wwaux | grep postfix:

root     11298  0.0  0.0  25112  1644 ?        Ss   10:39   0:00 /usr/lib/postfix/master
postfix  11347  0.0  0.0  37820  2340 ?        S    10:41   0:00 tlsmgr -l -t unix -u
postfix  12194  0.0  0.0  59352  4476 ?        S    12:04   0:00 smtpd -n smtp -t inet -u -c -o stress=
postfix  12195  0.0  0.0  27176  1536 ?        S    12:04   0:00 proxymap -t unix -u
postfix  12196  0.0  0.0  27176  1528 ?        S    12:04   0:00 anvil -l -t unix -u
gage     12487  0.0  0.0   9388   928 pts/7    S+   12:05   0:00 grep --color=auto postfix

output of netstat:

tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      11298/master
tcp        0      0 127.0.0.1:25465         0.0.0.0:*               LISTEN      2917/multicraft
tcp6       0      0 192.168.1.108:25569     :::*                    LISTEN      3791/java