smtp 587 always fails to send email

[Alice Bob]

Port number 587 always fails to send emails. The traces:

502 5.5.2 Error: command not recognized
502 5.5.2 Error: command not recognized
502 5.5.2 Error: command not recognized
500 5.5.2 Error: bad syntax
500 5.5.2 Error: bad syntax
500 5.5.2 Error: bad syntax

However I can connect to the smtp server on command line:

`gnutls-cli --verbose --crlf --starttls --insecure --port=587 smtp.zoho.com'

The relevant configs:

(setq send-mail-function 'smtpmail-send-it
      message-send-mail-function 'smtpmail-send-it
      smtpmail-default-smtp-server nil
      smtpmail-stream-type 'ssl
      smtpmail-smtp-service 587)
(setq smtpmail-smtp-server "smtp.zoho.com")

1. I am sure port 587 is allowed on firewall.
2. 587 fails for all different smtp servers (outlook etc.)

Could some guys give some hints?
-- 
horizon