Using an SMTP Relay (Recommended for Transactional Email)

For reliable email delivery, consider using an SMTP relay service instead of sending directly.

Configure Postfix to Relay

Add to /etc/postfix/main.cf:

relayhost = [smtp.provider.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt

Create credentials file:

echo "[smtp.provider.com]:587 username:password" > /etc/postfix/sasl_passwd
postmap /etc/postfix/sasl_passwd
chmod 600 /etc/postfix/sasl_passwd
systemctl restart postfix