Please point your mx record to the Inbound mx provided when registering for HES. It will look something like below :
If your domains is "domain.com" , your inbound mx record will be similar to domain.com.snwlhosted.com ( NOAM customers ) or domain.com.snwlhostedeu.com (EU customers)
Configure HES to allow all Emails to be routed through HES to your Mail server (Mail Server public Ip ) ( Inbound)
Login into the HES portal as admin
Go toSystem> Server Configuration> Inboundtab
UnderSettingsbox give your domain name in the box provided for relay domains
For theMail server Host name/ IPsection, Specify the FQDN or Public IP address of your Mail server
NOTE: Please add your mail server's FQDN or IP and no other IP in the text box (No ISP IPs or other external domains Public IP address)
Leave the Routing option toRound-robinand the save the settings
You are now configured to have inbound traffic routed form the internet to deliver to HES for domain.com that will then to you Public IP set for your mail server, which your firewall will nat and send the traffic to your internal IP address of your mail server to receive the inbound emails.
Be sure to have the Inbound Auditing on HES to track the inbound message being scanned by HES and delivered to O365.
On the message audit page, click Settings
Ensure the 'on' radio button is selected for Auditing inbound email