Help Desk Aheadworks setup guide

To set up a gateway for HDU:

1/ Example gateway using GMail:

It's recommended to enable `Delete Emails from Host`, it helps keep track when the email has been processed or not.

2/ Example gateway using Outlook: WIP

Behind the scenes, when cron job `aw_helpdesk2_process_gateway` runs, it pulls emails and create new entry(s) in table `aw_hd_gateway_email`

Another cron job, `aw_helpdesk2_process_email` processed that email and marked it with status 1