==== Required information ====
- iRedMail version: 0.8.7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): mysql
- Linux/BSD distribution name and version: Ubuntu 14.04 x64
- Related log if you're reporting an issue:
Dovecot.log:

Oct 26 20:39:46 auth: Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
Oct 26 20:39:46 auth: Debug: Module loaded: /usr/lib/dovecot/modules/auth/libdriver_mysql.so
Oct 26 20:39:46 auth: Debug: Wrote new auth token secret to /var/run/dovecot/auth-token-secret.dat
Oct 26 20:39:46 auth: Debug: passwd-file /etc/dovecot/dovecot-master-users-password: Read 0 users in 0 secs
Oct 26 20:39:46 auth: Debug: auth client connected (pid=2047)
Oct 26 20:39:46 auth: Debug: client in: AUTH    1       PLAIN   service=imap    secured session=zlF+xFwGNgB/AAAB        lip=127.0.0.1   rip=127.0.0.1   lport=143       rport=52790
resp=AHBvc3RtYXN0ZXIAa3Vrb3JpY2FqYW5jc2k= (previous base64 data may contain sensitive data)
Oct 26 20:39:46 auth-worker(2050): Debug: Loading modules from directory: /usr/lib/dovecot/modules/auth
Oct 26 20:39:46 auth-worker(2050): Debug: Module loaded: /usr/lib/dovecot/modules/auth/libdriver_mysql.so
Oct 26 20:39:46 auth-worker(2050): Debug: passwd-file /etc/dovecot/dovecot-master-users-password: Read 0 users in 0 secs
Oct 26 20:39:46 auth-worker(2050): Debug: sql(postmaster,127.0.0.1): query: SELECT password FROM mailbox WHERE username='postmaster' AND active='1'
Oct 26 20:39:46 auth-worker(2050): Info: sql(postmaster,127.0.0.1): unknown user
Oct 26 20:39:48 auth: Debug: client passdb out: FAIL    1       user=postmaster
Oct 26 20:39:48 imap-login: Info: Disconnected (auth failed, 1 attempts in 2 secs): user=<postmaster>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured, session=<zlF+xFwGNgB/AAAB>
Oct 26 20:40:00 auth: Debug: auth client connected (pid=2060)
Oct 26 20:40:00 auth: Debug: client in: AUTH    1       PLAIN   service=imap    secured session=OdxUxVwGOwB/AAAB        lip=127.0.0.1   rip=127.0.0.1   lport=143       rport=52795
resp=AHBvc3RtYXN0ZXIAa3Vrb3JpY2FqYW5jc2k= (previous base64 data may contain sensitive data)
Oct 26 20:40:04 auth-worker(2050): Debug: sql(postmaster,127.0.0.1): query: SELECT password FROM mailbox WHERE username='postmaster' AND active='1'
Oct 26 20:40:04 auth-worker(2050): Info: sql(postmaster,127.0.0.1): unknown user
Oct 26 20:40:06 auth: Debug: client passdb out: FAIL    1       user=postmaster
Oct 26 20:40:06 imap-login: Info: Disconnected (auth failed, 1 attempts in 6 secs): user=<postmaster>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured, session=<OdxUxVwGOwB/AAAB>

dovecot -n:

# 2.2.9: /etc/dovecot/dovecot.conf
# OS: Linux 3.13.0-32-generic x86_64 Ubuntu 14.04.1 LTS
auth_debug = yes
auth_debug_passwords = yes
auth_master_user_separator = *
auth_mechanisms = PLAIN LOGIN
auth_verbose = yes
dict {
  acl = mysql:/etc/dovecot/dovecot-share-folder.conf
  quotadict = mysql:/etc/dovecot/dovecot-used-quota.conf
}
first_valid_uid = 2000
last_valid_uid = 2000
listen = *
log_path = /var/log/dovecot.log
mail_debug = yes
mail_gid = 2000
mail_location = maildir:/%Lh/Maildir/:INDEX=/%Lh/Maildir/
mail_plugins = quota
mail_uid = 2000
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
namespace {
  inbox = yes
  location =
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    special_use = \Junk
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    auto = no
    special_use = \Sent
  }
  mailbox Spam {
    auto = no
    special_use = \Junk
  }
  mailbox Trash {
    auto = subscribe
    special_use = \Trash
  }
  prefix =
  separator = /
  type = private
}
namespace {
  list = children
  location = maildir:/%%Lh/Maildir/:INDEX=/%%Lh/Maildir/Shared/%%u
  prefix = Shared/%%u/
  separator = /
  subscriptions = yes
  type = shared
}
passdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
passdb {
  args = /etc/dovecot/dovecot-master-users-password
  driver = passwd-file
  master = yes
}
plugin {
  acl = vfile
  acl_shared_dict = proxy::acl
  auth_socket_path = /var/run/dovecot/auth-master
  quota = dict:user::proxy::quotadict
  quota_rule = *:storage=1G
  quota_warning = storage=85%% quota-warning 85 %u
  quota_warning2 = storage=90%% quota-warning 90 %u
  quota_warning3 = storage=95%% quota-warning 95 %u
  sieve = /%Lh/sieve/dovecot.sieve
  sieve_default = /var/vmail/sieve/dovecot.sieve
  sieve_dir = /%Lh/sieve
  sieve_global_dir = /var/vmail/sieve
}
protocols = pop3 imap sieve lmtp
service auth {
  unix_listener /var/spool/postfix/private/dovecot-auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-master {
    group = vmail
    mode = 0666
    user = vmail
  }
  unix_listener auth-userdb {
    group = vmail
    mode = 0660
    user = vmail
  }
}
service dict {
  unix_listener dict {
    group = vmail
    mode = 0660
    user = vmail
  }
}
service imap-login {
  process_limit = 500
  service_count = 1
}
service lmtp {
  executable = lmtp -L
  inet_listener lmtp {
    port = 24
  }
  process_min_avail = 5
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
  user = vmail
}
service pop3-login {
  service_count = 1
}
service quota-warning {
  executable = script /usr/local/bin/dovecot-quota-warning.sh
  unix_listener quota-warning {
    group = vmail
    mode = 0660
    user = vmail
  }
}
ssl = required
ssl_cert = </etc/ssl/certs/iRedMail_CA.pem
ssl_key = </etc/ssl/private/iRedMail.key
userdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
protocol lda {
  auth_socket_path = /var/run/dovecot/auth-master
  lda_mailbox_autocreate = yes
  log_path = /var/log/dovecot-sieve.log
  mail_plugins = quota sieve
  postmaster_address = root
}
protocol lmtp {
  info_log_path = /var/log/dovecot-lmtp.log
  lmtp_save_to_detail_mailbox = yes
  mail_plugins = quota sieve
  postmaster_address = postmaster
  recipient_delimiter = +
}
protocol imap {
  imap_client_workarounds = tb-extra-mailbox-sep
  mail_plugins = quota imap_quota
}
protocol pop3 {
  mail_plugins = quota
  pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
  pop3_uidl_format = %08Xu%08Xv
}

mail.log:

roundcube: IMAP Error: Login failed for postmaster from IP. LOGIN: Authentication failed. in /usr/share/apache2/roundcubemail-1.0.1/program/lib/Roundcu
be/rcube_imap.php on line 184 (POST /mail/?_task=login?_task=login&_action=login)

====

I can not login into Roundcube for postmaster and into iredadmin with postmaster@domain.com.