/dev/null

Client configuration (notebook, workstation what ever)

1. Edit your /etc/postfix/main.cf

# TLS client parameter
smtp_use_tls = yes
smtp_enforce_tls = yes
# for postfix < 2.3
# smtp_tls_security_level = secure
smtp_sasl_tls_security_options = $smtp_sasl_security_options
smtp_tls_CAfile = /etc/ssl/certs/cacert.org.pem
smtp_tls_loglevel = 0
[...]
relayhost = [mx1.example.com]:587
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
inet_interfaces = loopback-only
[...]
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwords
smtp_sasl_security_options = noanonymous

Setting [ and ] prevent the client from looking up the MX record for the domain. The port 587 is reserved for email clients. Some ISPs block port 25

2. Create your passwordmap – /etc/postfix/sasl_passwords

[mx1.example.net]:587 username:password

3. Run postmap for /etc/postfix/sasl_passwords

postmap /etc/postfix/sasl_passwords; rm /etc/postfix/sasl_passwords

Server configuration

1. Nothing if you have already a working mail server. That the user (/etc/postfix/sasl_passwords) must exists on the server is plausible ? Check your smtpd_*_restrictions on the mail server if the client won’t use sasl