MS365 Native domains require additional setup in MS365. You must create an IP allow list rule.
Note
Emails released from quarantine will be delivered via MX records.
To create an IP allow list rule:
In the Microsoft Exchange Admin Center, click Protection > Connection Filter.
Click the Edit button (pencil icon) to edit the default policy.
Click the Connection Filtering menu item and then click the + button in the IP Allow List section. A pop-up window appears.
These IPs are required to receive the alert notification and any other enabled notifications.
Enter the first IP address in the list below for the geographic region of your Email Cloud account. Then click the + button and enter the remaining IP addresses.
Email Security Region
IP Addresses
USA
3.93.93.0/24
EMEA
3.123.5.0/24
63.34.218.0/24
APJ
3.112.99.0/24
3.112.100.0/24
USGOV
15.200.32.0/24
CA
3.97.207.0/24
3.97.208.0/24
Click Save to save the rule configuration.
For authorization steps, go to Configuring authorizations.