Below is the steps required to delete junk email of your sync email on mobile phone:
1) Login to your Smartermail using the URL as 'mail.domainname.com.my'
2) On your left side choose Junk E-Mail
3) Right click on Junk Email
4) Then click 'Delete folder'
5) The Junk folder will not appear again.
Please be reminded that this steps can also be use to delete any other folders required on your Smarter Mail application.