Postfix: relay to authenticated SMTP.

Postfix: relay to authenticated SMTP.md

1. Taking Gmail as an example, put the following into /etc/postfix/main.cf.

    relayhost = [smtp.gmail.com]:587
    smtp_sasl_auth_enable = yes
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
    smtp_sasl_security_options = noanonymous
    smtp_sasl_mechanism_filter = plain
    smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt
    smtp_use_tls = yes
    smtp_tls_security_level = encrypt
   

   If the ca-bundle.crt does not exist, do (on OS X)

    sudo su
    mkdir -p /etc/pki/tls/certs/
    security find-certificate -a -p /System/Library/Keychains/SystemRootCertificates.keychain \
      >/etc/pki/tls/certs/ca-bundle.crt
   

2. Apparently you need to provide the credentials at some point.

    sudo echo '[smtp.gmail.com]:587 USERNAME@DOMAIN:PASSWORD' >>/etc/postfix/sasl_passwd
    sudo postmap /etc/postfix/sasl_passwd
   

   For added security, remove that sasl_passwd file after the postmap.

   Note that for two-step authentication you need to create an application-specific password.

3. And that's it! Reload Postfix:

    sudo postfix reload
   

   Or the more brutal way: stop followed by start.