the correct settings for a relay host
file:main.cf
############################################################
#relay host
############################################################
relayhost = [smtp.yoursmt.server]
############################################################
#SASL stuff
############################################################
#---/end
#enable SASL authentication
smtp_sasl_auth_enable = yes
#disallow methods that allow anonymous authentication.
smtp_sasl_security_options = noanonymous
#where to find sasl_passwd
#smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
#to prevent error with diction type
#run postmap /etc/postfix/sasl_passwd
#restrat postfix
smtp_sasl_password_maps = lmdb:/etc/postfix/sasl_passwd
#Enable STARTTLS encryption
smtp_use_tls = yes
#where to find CA certificates
#smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
#---/end
file:sasl_passwd
#---------------------------
#your smtp.com
#---------------------------
[smtp.yoursmt.server]:587 user:password
#---------------------------
brNP