main.cf の中身
relayhost = [smtp.hogehoge.ne.jp]:587
これに加えて
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/relay_password
smtp_sasl_security_options = noanonymous
を追記
/etc/postfix/relay_password を作成.中身は
smtp.hogehoge.ne.jp username:password
hash dbを作成
# postmap hash:/etc/postfix/relay_password
postfix の再読み込み
# /etc/init.d/postfix reload
gmailを使う場合のmain.cf
返信削除relayhost = [smtp.gmail.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/relay_password
smtp_use_tls = yes
smtp_sasl_security_options = noanonymous