/etc/postfix/sasl/smtpd.conf :
pwcheck_method: auxprop
auxprop_plugin: sql
mech_list: plain login cram-md5 digest-md5
sql_engine: mysql
sql_hostnames: 127.0.0.1
sql_user: user
sql_passwd: jelszó
sql_database: syscp
sql_select: select password from mail_users where username=’%u@%r’

/etc/postfix/main.cf
# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA’s job.
append_dot_mydomain = no

# Uncomment the next line to generate „delayed mail” warnings
#delay_warning_time = 4h

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache

#syscp
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no
append_dot_mydomain = no
myhostname = localhost
mydomain = localhost
mydestination = $myhostname $mydomain localhost localhost.$mydomain
mynetworks = 127.0.0.0/8
alias_maps = $alias_database
smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
virtual_mailbox_base = /var/kunden/mail/
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual_mailbox_maps.cf
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual_mailbox_domains.cf
virtual_alias_domains =
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual_alias_maps.cf
virtual_uid_maps = static:2000
virtual_gid_maps = static:2000
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes