compatibility_level=2
relayhost = [smtp.mailgun.org]:2525
smtp_sasl_mechanism_filter= AUTH LOGIN
smtp_sasl_password_maps = static:XXXXXXXXXXX:XXXXXXXXXXX
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
smtp_sasl_auth_enable = yes加入postfix資料夾中 main.cf 並且注意 最後的smtp_sasl_auth_enable = yes 因為這段碼沒設定導致無法正確驗證.