send mail directly using smtp ?

[William Xuuu]

Hi!

I have the following in my .gnus.el:

(require 'smtpmail)
(setq send-mail-function 'smtpmail-send-it
      message-send-mail-function 'smtpmail-send-it
      smtpmail-smtp-server "smtp.163.com"
      smtpmail-default-smtp-server "smtp.163.com"
      smtpmail-smtp-service 25
      smtpmail-auth-credentials '(("smtp.163.com" 25 "william_xuuu"
      "secret")))

(setq smtpmail-debug-info t)

When sending mail, i get an error: 

Sending...
Sending via mail...
220 Coremail SMTP(Anti Spam) System (163com[20030606])
250-smtp3
250-PIPELINING
250-AUTH LOGIN PLAIN NTLM
250-AUTH=LOGIN PLAIN NTLM
250 8BITMIME
553 You are not authorized to send mail as <MAIL FROM:
<william_xuuu@163.com>>, authentication is required
221 Bye
smtpmail-send-it: Sending failed; SMTP protocol error

Am i doing anything wrong? It's really very annoying when i can't use my
Gnus to send mail. Any help would be greatly appreciated.

-- 
William