Пример настройки работы Postfix через релэй с авторизацией наподобие krasmail.ru: /etc/postfix/main.cf relayhost = [krasmail.ru] # auth_krasmail smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_sasl_security_options = noanonymous smtp_sasl_type = cyrus smtp_sasl_mechanism_filter = login smtpd_sasl_path = smtpd /etc/postfix/sasl_passwd [krasmail.ru] user:password и потом postmap sasl_passwd postfix reload