SASL utlizando o dovecot.
  1. Editar o arquivo /etc/postfix/ Inserir as seguintes linhas:
    smtpd_sasl_auth_enable   = yes
    broken_sasl_auth_clients = yes
    smtpd_sasl_type          = dovecot
    smtpd_sasl_path          = private/auth
  2. Editar o arquivo /etc/dovecot.conf. Realizar as seguintes alterações:
    client {
          # The client socket is generally safe to export to everyone. Typical use
          # is to export it to your SMTP server so it can do SMTP AUTH lookups
          # using it.
          path = /var/spool/postfix/private/auth
          mode = 0660
          user = postfix
          group = postfix
  3. Reiniciar os serviços postfix e dovecot.