main.cf

# SASL - connection to Dovecot.
smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = /var/run/dovecot/auth-client
 
# Aliases LDAP
alias_maps = ..., ldap:/etc/postfix/aliases-ldap.cf

The Aliases user is kept in the attribute mail (class inetOrgPerson).

aliases-ldap.conf

server_host = ldapi://
bind = yes
bind_dn = uid=postfix,ou=System,dc=example,dc=com
bind_pw = haslo
version = 3
 
search_base = dc=example,dc=com
query_filter = (|(mail=%s@example.con)(mail=%s))
result_attribute = uid