mailx does not working

Hi
    i use mailx to send email from my linux, from today, it does not working, below is my shell command.

#!/bin/sh
mailx -s "Keer Server Monitor Report" -a /usr/local/nagios/var/nagios.log beardog1113@sina.com

    i also get the error log in my linux, seems my email has been rejected since it is junk email. my question is: how can i set the sender email address in mailx ? now, my email address is "root@localhost.localdomain", i would like change it to "cnserveradmin@keerok.com", then i will add SPF reocrd in my domain name "keerok.com", i think this will fix the junk email issue is that right?
    any other idea please let me know and thank you.
 

Final-Recipient: rfc822; beardog1113@hotmail.com
Original-Recipient: rfc822;beardog1113@hotmail.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx2.hotmail.com
Diagnostic-Code: smtp; 550 OU-002 (COL004-MC4F47) Unfortunately, messages from
    124.207.249.190 weren't sent. Please contact your Internet service provider
    since part of their network is on our block list. You can also refer your
    provider to http://mail.live.com/mail/troubleshooting.aspx#errors.